HUNDREDS of US marines were last night poised near the Taliban's final stronghold of Kandahar for a bloody showdown with the crumbling Afghan regime.

Cornered and facing annihilation, Taliban forces were dug in for a last stand as an advance force of 500 Americans were helicoptered into a desert airstrip in striking distance of their southern heartland - the first large scale deployment of ground troops in the war.

Another 1,000 US reinforcements are expected within the next 48 hours as the marines join the hunt for Osama bin Laden and his remaining Taliban allies. "The Marines have landed and we now own a piece of Afghanistan," said President George Bush last night.

"We're smoking them out, they're running and now we're going to bring them to justice,"

US Defence Secretary Donald Rumsfeld refused to be drawn on whether the marines were preparing for an assault on Kandahar alongside opposition forces, or would simply concentrate on hunting down bin Laden.

The news came as it emerged that the coalition had suffered its first casualties of the war - both British and American.

Defence Secretary Geoff Hoon told the Commons that four British troops - almost certainly members of the SAS - had been wounded inside Afghanistan while operating with US special forces at Mazar-e-Sharif.

All four are now back in Britain being treated for their injuries, although only one was said to have been seriously wounded.

Another five US soldiers were injured, three of them seriously, also at Mazar-e-Sharif when a bomb from a US plane fell too close to their position.

The US soldiers were injured in a battle for control of a mud-walled fortress near the city where 300 foreign Taliban prisoners, captured after the fall of Kunduz, seized weapons and turned on their guards.

Some of the prisoners were still holding out last night.

But as the noose on the main Taliban force at Kandahar tightens and opposition Pashtun tribesmen close in on the city, their leaders remain defiant.

Spokesman Mullah Abdullah said supreme leader Mullah Mohammed Omar was still in the city, in command of his troops, and "We have decided to fight against the American military until death."

Northern Alliance foreign minister Dr Abdullah Abdullah said he believed Omar and bin Laden were close together.

Despite the strengthening of the US garrison inside Afghanistan, Mr Hoon announced that the majority of the 6,000 troops on standby to go into the war torn country had been stood down.

Only 400 troops from the 2nd Battalion Parachute Regiment and the 16 Air Assault Brigade will be kept on heightened readiness to go, following a reassessment of the likely operational needs.