US troops in northern Kuwait have been fired at from two unidentified civilian vehicles, the US embassy in Kuwait said.

Jassem al-Hajeri was one of the two Kuwaitis killed

The American soldiers "did not return fire and there were no injuries," the embassy said.

It added that the US military and the Kuwaiti authorities were investigating the incident early on Monday near a training area.

Last Tuesday a US marine was killed and another was wounded in an attack by two Kuwaitis against troops training on a Kuwaiti island. Both attackers were killed.

The BBC's security correspondent Frank Gardner says there are growing signs that US forces and civilians in Kuwait face a bigger threat than was previously recognised.

US suspicions

Last week's attack was strongly condemned by the Kuwaiti Government and mainstream Islamist and other political groups.

The Kuwaiti authorities have been rounding up dozens of friends and relatives of the two attackers, but our correspondent says incidents are very embarrassing for the Kuwaiti Government.

US officials have already said that they suspect the marine's killers had links to al-Qaeda and received training in Afghanistan, despite denials by the Kuwaiti officials.

Washington also believes that the attacks were most likely to have been planned in Kuwait.

A further incident was reported last Wednesday, when US military personnel fired on a civilian vehicle north of the US base at Camp Doha, after apparently coming under threat from it.

The car was forced off the road, but the American vehicle did not stop.

Joint exercise

Some analysts believe that the most likely explanation is that the gunmen were two individuals who felt so angered by US policy towards Israel and the Palestinians that they decided to strike a blow for their beliefs.

Since 24 September, US marines have been taking part in training exercises in Kuwait amid reports that US forces are preparing for possible military action against Iraq.

There are already close to 10,000 fully equipped US troops in the country - as many as 1,000 of whom are taking part in the Eager Mace exercises.

Kuwait is the strongest regional supporter of US plans to topple Iraqi leader Saddam Hussein, but many Kuwaitis are nervous about a possible attack.

Our correspondent says that from now on, Americans living and serving in Kuwait are going to need eyes in the back of their heads.