Neither the White House nor the Pentagon would comment on the flights over Kabul, but Bush said in his weekly radio address, "The Taleban has been given the opportunity to surrender all the terrorists in Afghanistan and to close down their camps and operations. Full warning has been given, and time is running out."
The blunt warning was the clearest indication yet that the United States was poised to launch strikes not only against bin Laden and his al Qaeda followers but to punish the Taleban for not surrendering them.
Taleban leader Mullah Mohammad Omar said there was no case against bin Laden, whom the Taleban have been harbouring as a "guest" for several years.
The Taleban offered to release eight Western aid workers detained on charges of spreading Christianity to avert a US offensive. But Washington immediately rejected any deal.
In his radio address, Bush warned: "For those nations that stand with the terrorists, there will be a heavy price."
"In the struggle ahead, we will act in accordance with American ideals," he said. "We're offering help and friendship to the Afghan people. It is their Taleban rulers and the terrorists they harbour who have much to fear."
He said the Taleban had turned Afghanistan "into a sanctuary and training ground for international terrorists -- terrorists who have killed innocent citizens of many nations."
Omar, the spiritual leader of the Taleban, took a defiant line in a statement faxed to reporters in Kabul.
"Those who have perpetrated the attacks in the United States have left no traces behind them. If the United States thinks that the hijackers were the real culprits, then they have been killed," he said.
"No one will commit suicide on the orders of another or for the aims and interests of others," Omar said, adding that the United States should examine its own record in trying to find the "remedy" for the attacks last month.
US support for Israel and the presence of US troops in Saudi Arabia have been cited as factors fueling Islamic hostility toward America.
Washington has launched the biggest US military buildup since the 1991 Gulf War. US and British aircraft carriers, more than 300 warplanes, ships armed with cruise missiles and special forces troops have gathered within striking range of Afghanistan. Some 30,000 troops have been deployed.
After nearly four weeks of mounting tension in Central Asia, intense anti-aircraft fire erupted over Kabul on Saturday for about 15 minutes as gunners tried to bring down the two aircraft. One official said at least one of the planes was an unmanned surveillance drone.
Witnesses said a surface-to-air missile was also fired at the intruders. It was the first time anti-aircraft batteries had opened fire in the Afghan capital since test-firing several days ago sent residents scurrying for cover.
The Taleban linked the fate of eight detained Western aid workers to the US military preparations.
"If the United States mitigates the sufferings of the common people of Afghanistan and gives up its dire threats, then the Afghan government will also take steps to release the eight detained foreigners," a Foreign Ministry statement said.
Washington quickly rejected the offer. "These demands (to hand over bin Laden and his network) aren't subject to negotiations," a White House official said. "It is time for actions, not words."
Omar has ordered the release of British journalist Yvonne Ridley, who was arrested a week ago for entering Afghanistan illegally, the Afghan Islamic Press reported. She was expected to be released by Sunday.
Defence Secretary Donald Rumsfeld returned from a trip to the Middle East and Central Asia, and White House officials said Bush was satisfied with the cooperation being given by a number of countries there, including Pakistan, Uzbekistan, Oman, Qatar, the United Arab Emirates and Saudi Arabia.
Taleban officials threatened on Saturday to attack neighbouring Uzbekistan if it aided the United States in pursuing bin Laden.
"We will attack Uzbekistan if any attack is launched from its borders," Radio Voice of Shariat quoted officials as telling a rally in Hairaton, near the Uzbek border.
Uzbekistan's president, Islam Karimov, said on Friday that he would make an air base available for use by US cargo planes, helicopters and troops, but only for humanitarian and rescue operations.
- REUTERS
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