The US strengthened its coalition on Tuesday when Saudi Arabia, one of only two Arab countries to have recognised Taleban rule, announced it was severing diplomatic ties with the regime.
Pakistan is now the only country to recognise the Taleban, which faces imminent attacks by US-led forces over its refusal to hand Bin Laden over.
US President George W Bush has been briefing leaders of Congress on the US military deployments within striking distance of Afghanistan, telling them not to expect a conventional war.
He also discussed co-operation with the visiting Japanese Prime Minister Junichiro Koizumi.
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The Saudi decision to sever relations comes three days after the United Arab Emirates, the other Arab state to have recognised the Taleban, severed ties with Kabul.
The kingdom said it would continue to stand by fellow Muslims in Afghanistan.
The Saudi Government is still apparently resisting US pressure to allow American fighter planes to use its bases for an attack on Afghanistan.
Correspondents say this is one of the most serious sticking points in the building of the US coalition that includes the Gulf States.
Pakistani President Pervez Mursharraf has denied he is under international pressure to sever ties with the Taleban authorities, adding that he could see no requirement to break the relationship.
Russian support
Earlier, US Secretary of State Colin Powell welcomed a Russian offer of support for US operations in Afghanistan, including the use of former Soviet airbases in central Asia.
Mr Powell said he was "very pleased" with Russian President Vladimir Putin's offer to widen cooperation in the fight against terrorism.
President Putin has further increased the pressure on the Taleban by saying that Russia would offer more arms and other supplies to the Northern Alliance, the group fighting the Taleban in northern Afghanistan.
The BBC's correspondent in Moscow, Caroline Wyatt, says Mr Putin's most important offer to the US was to allow it and its allies to use former Soviet airbases in the countries surrounding Afghanistan.
Mr Putin said that those states, including Uzbekistan, Tajikistan and Turkmenistan, shared Russia's position.
And Russia will offer further pooling of intelligence, the president said, prior to leaving on a visit to Germany on Tuesday.
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