The council, or loya jirga, was supposed to start Monday; the opening was reset for Tuesday afternoon.
U.S. special envoy Zalmay Khalilzad blamed the delay on confusion caused by reports that the former monarch, Mohammad Zaher Shah, would be a candidate for head of state, which the loya jirga is to choose.
Diplomatic sources also blamed a dispute within the Afghan leadership over the role of the former king, Mohammad Zaher Shah. The historic meeting, or loya jirga, was to have opened Monday morning to select a new government to run the country pending elections in 18 months.
However, a member of the organizing commission, Abdul Salam Rahimi, told reporters the loya jirga would open at 3 p.m. Tuesday "due to logistical and preparatory work that was going on and was not completed on time."
Meanwhile, U.S. special forces have uncovered several large caches of weapons in southeast Afghanistan, including 30 surface-to-air missiles and a cave where eight truckloads of ammunition were hidden, a spokesman said.
It was not yet known if the stashes had been left by al Qaeda or Taliban fighters being hunted by U.S.-led forces in the region near the Pakistani border, U.S. Col. Roger King said Monday.
"But every time we find one of these caches it degrades the enemy's ability to operate and increases security for the country of Afghanistan," King told reporters at Bagram air base, headquarters for the U.S.-led campaign.
The weapons caches in southeast Afghanistan were uncovered in the last days of May, King said. In a cave near the town of Khost, special forces troops found two armored vehicles and eight truckloads of weapons and hundreds of thousands of rounds of ammunition, he said. The 30 Chinese-made HN5S surface-to-air missiles were found two days earlier near the town of Gardez.
U.S. officials have said al Qaeda or Taliban fighters may try to shoot down a coalition helicopter as a high-profile, "symbolic" attack against troops in Afghanistan.
Special forces near the border have been trying for weeks to track down traces of the Taliban and al Qaeda, many of whose members have reportedly taken refuge in Pakistan. With few fighters to be found, troops have been turning up weapons caches.
Troops also found a collection of mortars, rockets and machine gun ammunition in the village of Organi and a stash of grenades, rifles and armor-piercing ammunition near Lwara village in the last days of May, King said.
For the loya jirga, Kabul is crawling with international security, blanketed by a new police force and protected by a freshly deployed national guard. Security forces are bracing for anything as Afghanistan begins a crucial week of charting the future.
Leaders of the northern alliance, who dominate the current interim regime, strongly oppose any role for Zaher Shah in the government to be chosen by the council, or loya jirga. Zaher Shah is to convene the council.
A U.N. official, who did not want to be identified, said the number of delegates has grown to around 1,600 from an earlier expected 1,501 and that this could also be one of the issues factions were discussing.
Also Monday, military inspectors completed tests at a U.S. base in Uzbekistan where traces of nerve gas and mustard gas were detected last week at sites near where U.S. troops were working.
No new contaminated sites were found at the base, King said. But in a hangar where mustard gas traces were earlier found, the inspectors on Sunday turned up traces of what could be a "blood agent," a chemical weapon — like cyanide, for example — that prevents cells from absorbing oxygen.
King said further tests were being made, noting that the traces could actually be rocket fuel, which has a similar composition to some types of blood agents and has caused confusion in past tests.
The nerve and mustard contaminations at Khanabad air base are thought to be caused by chemical weapons once stored there by the Soviet military, before Uzbekistan gained independence in 1991. But officials are still trying to determine the exact sources.
U.S. troops have been moved away from the contaminated sites, and no one has reported symptoms of exposure to the agents, King said.
In other developments: