According a UN spokesman in Kuwait, in an account later confirmed by the State Department here, the two men crossed through United Nations- manned border posts en route to the UN's Kuwait-Iraq Observer Mission (Unikom) in the southern Iraqi town of Umm Qasr, where they arrived at around 7.45pm on 13 March.
But they were refused entry because they had no authorisation and were told to return to Kuwait. On the way back they were apparently arrested by Iraqi police and taken to an unknown destination. The US Embassy in Kuwait has enlisted the aid of both the UN and the Polish government, which has normal relations with Iraq, to secure their release.
The original low-key handling of the affair suggests that Washington had been hoping to settle it quietly. But as the days dragged by without progress, that approach perforce changed. President Clinton has now been briefed, and White House spokesman Mike McCurry told reporters Washington was doing everything possible to secure the men's release.
Although the identity of the two men has not been made public, they are known to be US civilians under contract to Unikom. But it was not clear how they managed to stray through the border checkpoints - apparently the first to do so since 1994 when Kuwait completed work on a trench and 13ft rampart along the previously unmarked frontier.
Such unwitting mistakes can have unpleasant consequences, with several Westerners who strayed into Iraq receiving jail terms of up to eight years for espionage (although they have generally been freed after a year or so). And Baghdad has less reason than ever at this particular moment to be kindly disposed towards the US.
The incident comes just a fortnight after a failed coup against Saddam Hussein, apparently led by the head of the Iraqi military intelligence service during the Gulf war, which ended with Saddam's forces being driven from Kuwait by a US-led coalition. In its first acknowledgement of the coup, the Baghdad authorities declared yesterday the government "could withstand any US-backed bid" to topple it.
Further ground for resentment came last week when Washington succeeded in persuading a clear majority of the UN Security Council to maintain the 1991 oil embargo against Iraq - overcoming strenuous opposition from France and Russia and denying Saddam access to a vital source of export earnings.