Mikhail Saakashvili, speaking to foreign reporters in the capital in an appeal for international help, said the convoy was about halfway between the western cities of Senaki and Kutaisi.
"We have no idea what they're doing," Georgian Prime Minister Lado Gurgenidze said of the Russian column. "One explanation could be they are trying to rattle the civilian population."
There was no immediate response from Russia to the claims. Both sides have made conflicting statements since fighting broke out Aug. 7, when Georgia sought to retake the breakaway province of South Ossetia.
According to two defense officials, the latest Pentagon information does not show any major movement by Russian troops or tanks Thursday. The officials said that if tanks are moving toward Kutaisi, the Russian troops might be headed to South Ossetia where they're supposed to be going.
The developments came on a day that Russian troops searched selected cities, forests and fields in Georgia looking for military equipment abandoned by Georgian forces during the week-old war. And Russia's foreign minister declared Georgia could "forget about" regaining two separatist provinces.
In Washington, Defense Secretary Robert Gates said he saw no need to invoke American military force in the war between Russia and Georgia but warned that U.S.-Russian relations could suffer lasting damage if Moscow doesn't retreat.
"The United States spent 45 years working very hard to avoid a military confrontation with Russia," said Gates. "I see no reason to change that approach today."
Gates was adamant that sending U.S. troops is not an option, but the U.S. already had a number of its most elite Special Operations Forces on the ground in Georgia, assisting and training the Georgian army, reports CBS News chief foreign affairs correspondent Lara Logan.
That would put them in position to advise the Georgians in the current crisis, military and intelligence sources told CBS News.
Thursday's events presented a huge challenge to the EU-sponsored cease-fire agreement designed to end seven days of fighting that began after Georgia tried to regain control of South Ossetia. The accord had envisioned Russian and Georgian forces returning to their original positions.
"One can forget about any talk about Georgia's territorial integrity because, I believe, it is impossible to persuade South Ossetia and Abkhazia to agree with the logic that they can be forced back into the Georgian state," Russian Foreign Minister Sergey Lavrov told reporters as Russia's president met in the Kremlin with the two separatist leaders. The comments and meeting were a clear sign that Moscow is considering the enclaves.
The Bush administration said it will ignore the "bluster" from Russia about the separatist regions. However, Secretary of State Condoleezza Rice headed to Georgia to ask the U.S. ally to sign a cease-fire agreement with Russia that includes apparent concessions to Moscow but preserves Georgian borders, a U.S. official said.
The pact fleshes out a French-brokered agreement giving Russian peacekeepers the express right to patrol beyond South Ossetia, the disputed border region at the heart of the conflict.
The official, speaking on condition of anonymity because the pact is not finalized, said there are important clarifications still to be made and the U.S. would support more powers for the Russian peacekeepers only if they were limited, well defined and temporary.
Still, analysts said there were holes in the EU plan to end the war between Georgia and Russia.
Robert Hunter, former ambassador to NATO under President Clinton, said the EU plan has halted much of the fighting but hardly commits the Russians to much.
"As it stands, this proposal leaves the Russians in total control," he told the AP in New York. "There is nothing in here about the inviolability of Georgia's frontiers," which he said lets Russia move forward on absorbing the separatist regions.
The war has raised concerns among other former Soviet bloc nations. On Thursday, Poland and the United States reached an agreement that will see a battery of American missiles established inside Poland.
"Poland and the Poles do not want to be in alliances in which assistance comes at some point later - it is no good when assistance comes to dead people. Poland wants to be in alliances where assistance comes in the very first hours of - knock on wood - any possible conflict," Prime Minister Donald Tusk said.
Relief planes swooped into the Georgian capital of Tbilisi with tons of supplies for the estimated 100,000 people uprooted by the fighting. U.S. officials said the two planes carried cots, blankets, medicine and surgical supplies - but the Russians insinuated that the U.S. might have sent military aid as well.
Russia's deputy chief of General Staff Col.-Gen. Anatoly Nogovitsyn said he wasn't sure that the U.S. planes carried only humanitarian cargo. "It causes our concern," he said.
U.S. officials rejected the claim.
Georgia, bordering the Black Sea between Turkey and Russia, was ruled by Moscow for most of the two centuries preceding the 1991 breakup of the Soviet Union. Russia has distributed passports to most in South Ossetia and Abkhazia and stationed troops they call peacekeepers there since the early 1990s.
Georgia's Interior Ministry accused Russia of using Iskander short-range missiles on the Black Sea port of Poti and in the central city of Gori. Ministry official Shota Utiashvili showed reporters images of what he said were shrapnel and remains of the missiles.
Russian troops and Georgian troops briefly patrolled Gori together Thursday before relations between the sides broke down and the Georgians left. At least 20 explosions were heard later near Gori, along with small-arms fire. It was not clear whether it was renewed fighting or the disposal of ordnance from a Georgian military base.
Gori, battered by Russian bombing before Tuesday's cease-fire, lies on Georgia's main east-west road only 60 miles west of Tbilisi.
Terrified Georgians had to flee their village near Gori on foot, they said, because rampaging militias from South Ossetia are burning homes and farms, killing people and livestock, reports CBS News correspondent Mark Phillips.
Earlier, at a checkpoint outside Gori, Georgian Interior Minister Vano Merabishvili said Georgian engineers and special forces were searching for Russian mines. "We are cleaning roads because we have information that there are some mines," he told AP.
A Russian envoy denied that any roads around Gori were mined.
AP television footage showed Russian troops inside and outside Gori, with plumes of black smoke rising from behind a forest.
Nogovitsyn said Russian troops went into Gori to establish contact with its civilian administration and to take control over military depots abandoned by the Georgian forces. "The abandoned weapons needed protection," he said.
Danish journalists said drunken South Ossetia militiamen fired shots into the ground before them and a UNHCR representative Thursday as Russian tanks blocked them from entering Gori. One journalist's television camera was seized.
In Vienna, Victor Dolidze, Georgia's ambassador to the Organization for Security and Cooperation in Europe, said Russian troops were looting the Georgian military base in Senaki, as well Poti.
The Russian envoy to the OSCE, Vladimir Voronkov, strongly denied Dolidze's other claim, that Russian troops had laid mines in Gori and may be doing the same in Senaki and Poti.
An AP Television News crew heard explosions Thursday at a military base in Senaki and were told by officials from both sides that the Russians were destroying ordnance. Dozens of Russian armored vehicles and troops later set up for the night on the main road from Senaki north to Zugdidi.
Russian troops operated with confidence Thursday in and around Poti, the site of Georgia's key oil terminal. Georgia's coast guard said Russian troops burned four Georgian patrol boats in Poti on Wednesday, then returned Thursday to loot and destroy the coast guard's radar and other equipment.
Georgian port authorities told an AP television crew in Poti that Russian troops were at the Poti docks early Thursday and APTN saw a destroyed Georgian military boat about 60 feet long.
The same APTN crew followed Russian troops on the outskirts of Poti as they searched a field and a forest at an old Soviet military base for possible Georgian military equipment.
Nogovitsyn would not comment on the Russian presence in Poti, saying only that Russian forces were operating within their "area of responsibility." He also shrugged off as "nonsense" Ukraine's order restricting Russia's navy from moving freely in Ukraine's Black Sea waters.
Another APTN camera crew saw Russian soldiers and military vehicles parked Thursday inside the Georgian government's elegant gated residence in the western town of Zugdidi. Some of the Russian soldiers wore blue peacekeeping helmets, others wore green camouflage helmets, all were heavily armed. Other Russian troops patrolled the city.
"The Russian troops are here. They are occupying," Ygor Gegenava, an elderly Zugdidi resident told the APTN crew. "We don't want them here. What we need is friendship and good relations with the Russian people."
The United Nations estimates 100,000 people have been uprooted by the fighting, including 12,000 South Ossetians who fled north into Russia.
In Tbilisi, displaced Georgians set up tents at a makeshift refugee camp, hanging washing on lines and rolling out mattresses and bedding.
"We have no beds, six of us are sleeping on the floor. We don't have anything left," a Georgian woman named Manana told an APTN crew. She would not give her last name, fearing reprisals.