WASHINGTON/ISLAMABAD (Reuters) - Taliban gunners fired fierce volleys at two aircraft flying high over Kabul on Saturday in what appeared to be a spy mission before an expected U.S.-led war on the Osama bin Laden network and its Afghan protectors. 
President Bush warned Afghanistan's hard-line Islamic rulers that time was running out for them to surrender bin Laden, but Taliban leader Mullah Mohammad Omar said there was no case against the Saudi exile. 
The Taliban sought to use eight detained Western aid workers as bargaining chips to avert a U.S. offensive, but Washington immediately rejected any deal. 
Pakistan said it had no plans to intercede further to try to avert the conflict, set in motion when hijackers flew three aircraft into the World Trade Center and the Pentagon on Sept. 11. About 5,600 people were killed in those attacks and the crash of a fourth hijacked jetliner in Pennsylvania. 
Bush, in his weekly radio address, said the Taliban had had the opportunity to shut down bin Laden's al Qaeda network -- which the United States accuses of being behind the attacks -- but had not taken it. 
An explosion rocked the Saudi city of al-Khobar, killing two foreigners and wounding four, but Bush administration officials said they saw no immediate connection between the blast and the U.S. efforts to build a coalition to take on the Taliban and al Qaeda. 
The official Saudi Press Agency said details of the blast at an electronics shop were still sketchy. Khobar was the scene of a truck bomb that killed 19 U.S. soldiers in 1996. 
In his radio address, Bush warned: "Full warning has been given, and time is running out. ... 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 Taliban rulers and the terrorists they harbor who have much to fear." 
Bush said the Taliban had turned Afghanistan "into a sanctuary and training ground for international terrorists -- terrorists who have killed innocent citizens of many nations." 
Pakistan, the only nation to maintain diplomatic ties with the rulers of neighboring Afghanistan, echoed the U.S. warning about bin Laden. 
"The Taliban know what the international community expects of them," said Pakistani Foreign Ministry spokesman Riaz Mohammad Khan. "If they decide to respond to what the international community wants ... it is to their advantage to do so." 
The spokesman said Pakistan had no plans to make new diplomatic overtures to the Taliban, who are seeking to portray the U.S.-led campaign against them as an assault on Islam. 
Omar, the spiritual leader of the Taliban, 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. 
U.S. support for Israel and the presence of U.S. troops in Saudi Arabia have been cited as factors fueling Islamic hostility toward America. 
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 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. 
There was no immediate comment on the flights from the Pentagon, which has begun a major military buildup in the region as it prepares to retaliate for the attacks last month. 
The Taliban linked the fate of eight detained Western aid workers to the U.S. 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. 
British Prime Minister Tony Blair, back in Britain after visiting Pakistan and India on a tour aimed at bolstering support for the U.S.-led coalition, said coalition members had the will and the capacity to act. 
"The trap is being set around the Taliban regime in the sense that we are cutting off their sources of financing and supply and we have built a very strong diplomatic and political coalition in the area," Blair said. 
PROTESTS TARGET BRITAIN, U.S. 
Up to 4,000 people staged protests against Blair and the United States in the Pakistani city of Peshawar on Saturday. 
"We declare war on America and Britain," said one speaker from the Jamiat-e-Ulema Islam, which has said it has started recruiting fighters to go to Afghanistan if the United States attacks. 
In Washington, G7 finance ministers from leading industrial nations gathered to discuss ways of financially starving groups responsible for terrorism and of limiting damage to their economies from the Sept. 11 attacks. 
In Geneva, donor countries pledged sufficient funds for a $584 million U.N. emergency appeal for Afghanistan. 
U.N. emergency relief coordinator Kenzo Oshima said countries promised $608 million during a two-day meeting of the U.N.-sponsored Afghan Forum but some of the funds would be paid to non-U.N. relief groups. 
Defense 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. 
America has launched the biggest U.S. military buildup since the 1991 Gulf War. U.S. and British aircraft carriers, more than 300 warplanes, ships armed with cruise missiles and special forces troops have gathered within striking range. About 30,000 troops have been deployed. 
Taliban officials threatened on Saturday to attack neighboring 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 U.S. cargo planes, helicopters and troops, but only for humanitarian and rescue operations.