The United States is pressing ahead with a major military build-up in the Gulf in preparation for a possible war with Iraq.

Thousands of soldiers are being deployed to the region this week, joining the 50,000 already there.

The White House has also ordered the aircraft carrier USS Abraham Lincoln to abandon its voyage home and return to Australia, fuelling speculation that plans are being made to use the vessel in a campaign.

The giant US Navy hospital ship, USS Comfort, also left her home port of Baltimore on Monday and is thought to be heading to Diego Garcia in the Indian Ocean.

The build-up has mounted as United Nations weapons inspectors continue to search Iraq for the weapons of mass destruction which Washington insists Baghdad possesses.

Nothing suspicious has yet been found, they say.

Gulf veterans

Britain, America's ally on the issue of Iraq, is also expected to announce that the helicopter assault ship HMS Ocean will be deployed later this month with Royal Marines aboard.

The Comfort has 12 operating theatres

It is also expected to mobilise 7,000 reservists.

In the US, at least 10,000 reservists have been told to prepare for possible overseas deployment as early as this week to support the build-up.

The US Army has also started deploying more than 11,000 soldiers from the 3rd Infantry Division in Fort Benning and Fort Stewart in Georgia - specialists in desert warfare.

Correspondents say that many of these troops are veterans from Desert Storm, the US-led military operation to remove the Iraqi army from Kuwait over 10 years ago.

Taking to the water

The USS Tarawa has also set sail from San Diego with 4,000 marines and sailors on board in a six-month tour that will put them within striking distance of Iraq.

The USS Comfort, the medical boat, meanwhile left with about 300 of a total crew of more than 1,000 aboard from Baltimore on Monday.

Most staff will only be flown out to join the vessel if war looks imminent.

She can handle up to 1,000 casualties at a time, has 12 operating theatres and is equipped to deal with the effects of chemical and biological attacks.

The BBC's Nick Childs at the Pentagon said her departure was the clearest signal yet that a new phase in the US build-up was under way.

But Pentagon officials insist the number of deployment orders issued so far still account for only about half of the 50,000 or so reinforcements originally expected at this stage.

Our correspondent says the Pentagon still seems to be pacing its preparations for war to increase the pressure on Baghdad on one hand, while keeping options open on the other.