US Secretary of State Colin Powell, on a landmark trip to Kabul on Thursday, said Washington would stand by Afghanistan and vowed to eradicate Islamic extremists in the country.

As US warplanes scoured the land for remnants of Osama bin Laden's al Qaeda network and the former ruling Taliban, Powell told Afghanistan's new leaders his government planned a significant contribution to the country's reconstruction.

In the southern city of Kandahar, US Marines questioned a man who said he was a key financial backer of the Taliban, but there was still no word on the whereabouts of Bin Laden and his protector, vanquished Taliban leader Mullah Mohammad Omar.

And far away in the Philippines, the United States opened a new front in its war on terrorism, setting up camp on a southern island where they will join operations against Muslim rebels suspected of links to bin Laden.

Powell, on an Asian tour dominated by confrontation between India and Pakistan, was the highest ranking US leader in the Central Asian country since then Secretary of State Henry Kissinger stopped there in 1976.

"We will be with you in this current crisis and for the future," Powell told a joint news conference with Afghanistan's interim leader, Hamid Karzai.

"We are committed to doing everything we can to assist you in this time of transition to a new Afghanistan, an Afghanistan where people will be able to live in peace and security."

The World Bank estimates Afghanistan's reconstruction will cost $15 billion over 10 years.

Karzai diplomatically reminded Powell that many Afghans wondered whether Washington would abandon them after full victory over the Taliban leadership, as it did after US-backed rebels drove Soviet troops out in 1989.

"In all our meetings with the Afghan people, they ask us - 'Is the United States committed? Will they stay with us?'," said Karzai, who wore his trademark bright green Uzbek robe and Persian lamb hat.

"Now I can tell them, 'Yes, the US will stay with us'."