The largest military build-up since the Gulf war in 1991 continued on Sunday as the US positioned forces in readiness for strikes on Afghanistan.

"What we've been doing is getting our capabilities located, positioned, arranged around the world so that at that point where the president decides that he has a set of things he would like done, that we will be in a position to carry those things out," Donald Rumsfeld, defence secretary told CBS television.

The US has kept quiet about its war plans. But much of the ground combat in the hostile mountainous terrain is expected to be carried out by elite special forces. There were unconfirmed reports that some US and British units were already positioned.

Mr Rumsfeld said the US had lost contact with an unmanned aircraft over Afghanistan but had "no reason to believe" the aircraft was brought down by Taliban fighters, as claimed.

Some 350 US aircraft, bombers and fighters are in the region and more are on their way. Heavy B-1 and B-52 bombers and A-10 Warthog attack aircraft, designed for air support of ground forces, have left bases in the US.

The US assault ship Essex joined the aircraft carrier Kitty Hawk in leaving its Japanese base for the Indian Ocean. The US already has groups positioned in the Gulf, the Arabian Sea and the Mediterranean.

Authorities in Uzbekistan, on Afghanistan's northern border, confirmed over the weekend that US military aircraft had arrived there. Transport craft landed on Saturday at an airfield outside of the capital Tashkent, officials told Agence France-Presse.

The Russian news agency Interfax, quoting "informed sources", said that two C-130 transport aircraft unloaded a cargo of equipment, including intelligence-gathering devices, and about 100 servicemen.

Two batches of Royal Air Force Tornado fighters left for the Gulf, adding to the British military build-up.

Pakistan reinforced its military position along its sealed border with Afghanistan after reports that the Taliban was stepping up military preparations.