Deputy Secretary of State Richard Armitage described Iraq as a "war zone," but noted that "we have the momentum in this process."
"I'm absolutely convinced we have a very solid plan to go out and get these people who are killing us and killing Iraqis," he told reporters during a visit to Iraq.
The sharp rise in the number of attacks against the troops of the U.S.-led coalition and their allies in the Iraqi security services, and the guerrillas' apparent ability to strike at will, has prompted fears that the initiative in the conflict is slipping from the coalition's hands.
During a news conference in the heavily guarded compound housing the Iraq's U.S.-led administration, Armitage appeared anxious to ease such fears.
"I'm pretty convinced after this short visit ... that we will take this fight to the enemy," he said.
Later Saturday, detonations were heard in Baghdad. An Iraqi police officer, Maj. Kadhim Abbas Hamza, said a mortar shell exploded in the yard in front of the main railway station and there were no casualties.
At the same time, coalition troops blocked traffic across the Jumhuriya Bridge near the U.S. command compound known as the "Green Zone." For the first time since the end of major combat in May, U.S. jets and helicopters circled overhead through the night sky with their navigation lights turned off.
Two soldiers of the 82nd Airborne Division died Saturday when a homemade bomb exploded beside their vehicle about in Fallujah, a center of Sunni Muslim resistance 40 miles west of Baghdad, the military said.
Their deaths brought to 34 the number of American soldiers who have died in Iraq in November as resistance has escalated during the Islamic holy month of Ramadan. The death toll for the week was by far the largest for any seven-day period since President Bush declared the end of major combat on May 1.
In Geneva, the International Red Cross said Saturday it was temporarily closing its offices in Baghdad and Basra because of the security situation. The Red Cross had planned to cut back on its foreign staff of 30 people after the Oct. 27 truck-bombing at its Baghdad office but wanted to keep the offices open with reduced staff.
In other developments:
The U.S. military on Saturday unleashed a show of force in Saddam Hussein's hometown of Tikrit, rocketing buildings to rubble and dropping 500-pound bombs near the site where a Black Hawk helicopter crashed.
The pre-dawn barrage came hours after the Black Hawk — apparently shot down by insurgents — exploded in flames in a grassy field just outside Tikrit, a hotbed of anti-American sentiment. Six Americans in the copter died, capping the bloodiest week in Iraq for U.S. forces since the fall of Baghdad.
In retaliation, U.S. rocket and heavy machine gun fire destroyed a warehouse and two houses believed to have been used as hideouts by militants. Air Force fighters screeching overhead dropped bombs, which rattled houses. Mortar rounds howled, and tracer bullets lit up the sky.
"We want to remind this town that we have teeth and claws and we will use them," said Lt. Col. Steven Russell of the 4th Infantry Division, who led raid in Tikrit, a city of 120,000 people about 120 miles north of Baghdad.
CBS News Reporter D'Agata says, after pounding the hills around Tikrit with air strikes from F-16 fighter jets, followed by rounds from Abrams tanks and Bradley Fighting Vehicles, ground troops launched pre-dawn raids throughout Tikrit, netting 16 people.
The Army said five Iraqis were killed in fighting: three suspected of firing missiles into the US compound, one in a gunfight, and another who shot at troops after being caught trying to string decapitation wire across a road. The Army said no Iraqi civilians were killed in the attacks.
D'Agata says, "The scale and force of the military bombardment was clearly aimed at rattling guerrillas in the region, but it may inflame otherwise peaceful local Iraqis. The attack began on a Friday -- a Muslim day of rest -- during the Holy Month of Ramadan." He added that the reimposition of the curfew won't win any fans among Tikrit resident, either.
D'Agata says the commanding officer in Tikrit confirmed on Saturday what most already suspected: that it was hostile fire, a rocket-propelled grenade, that brought the Black Hawk down, the third U-S helicopter to fall to enemy fire in two weeks.
But the U.S. command said in a statement Saturday that initial findings "discount the use of surface-to-air missiles as a possible cause" of the Black Hawk crash.
U.S. officers have long been concerned about the safety of aviation because of the hundreds, perhaps thousands, of shoulder-fired missiles missing in Iraq after the collapse of Saddam's regime in April.
On Oct. 25, insurgents shot down a Black Hawk over Tikrit, injuring one crewman. On Sunday, gunners brought down a Chinook transport helicopter west of Baghdad, killing 16 Americans in the bloodiest single strike against U.S. forces since the war began March 20. An Apache attack helicopter was shot down in June, but the two crewmembers escaped injury.