Washington called last night for an emergency meeting of the United Nations Security Council to discuss the movements, as it did during the Iraqi troop build-up which preceded the 1990 invasion of Kuwait.
President Bill Clinton warned President Saddam that the United States was taking the 'necessary steps' to deal with the threat of troops close to the border, and said Washington's resolve was as strong as it had been during the Gulf war.
The Saudi Foreign Minister, Saud al-Faisal, met Mr Clinton yesterday and told him US aircraft would be allowed to use Saudi airfields in response to Iraq's military build-up.
Pentagon officials said the aircraft carrier George Washington was being sent from the Mediterranean to the Gulf region, extra weapons were on their way from the Indian Ocean island of Diego Garcia, and army units in the US were being put on alert.
There are already some 12,000 US troops in the wider Gulf area, including those in Turkey and Saudi Arabia. Four vessels already in the Gulf have a total of 2,000 Marines. Allied airpower, predominantly American, is put at some 140 planes. Kuwait has mobilised reserve units.
In Britain, a joint statement by the Foreign Office and the Ministry of Defence said Kuwait had made a formal request for assistance under a bilateral defence agreement. In response, the frigate HMS Cornwall, which is in the Gulf as part of the Royal Navy's Armilla Patrol, will arrive off Kuwait tomorrow morning.
Military experts in London and at Nato headquarters in Brussels said it was unclear whether Iraq intended to invade Kuwait, or whether it wanted to provoke the West by maintaining a threatening presence on the border.
Earlier this week, Iraq demanded a specific deadline for the easing of sanctions if the UN expected Baghdad's continuing co- operation in scrapping and monitoring its weapons potential, as required by resolutions adopted after the Gulf war.
Yesterday's build-up came shortly before warnings at the UN by Tariq Aziz, Iraq's deputy prime minister, who called on the international community to examine the 'iniquitous and illegitimate situation' under which he said one or two major powers were preventing the lifting of sanctions.
The newspaper of the ruling Baathist party, al-Thawra, railed against the embargo, adding: 'No one in the world would blame the Iraqi people and its leadership if they embarked on measures . . . which will give enemies a lesson.'
Although US officials say the forces involved - several brigades of the elite Republican Guard, according to most accounts - were smaller than those used to invade Kuwait, Mr Clinton told a news conference that Washington was watching events very closely and would respond as required.
The President urged his audience not to 'inflame this situation beyond the facts' but said it would be a 'grave mistake' for President Saddam to believe US determination has weakened.
In a statement, the US State Department said: 'Confrontational tactics will prove no more successful now than in the past,' referring to the 1991 war in which the US and allied nations forced Iraq to reverse its annexation of Kuwait.Reuse content