The US State Department warned Americans in Saudi Arabia on Thursday of a possible terror attack in the Red Sea port city of Jeddah.

"The US consulate general in Jeddah has received an unconfirmed report that a possible terrorist attack in the Al Hamra district of Jeddah may occur in the near future," the State Department said in a statement.

The State Department advised US citizens in Saudi Arabia to maintain a high level of vigilance and to take steps to increase their security.

A variety of intelligence indicates potential Al Qaeda related plots to attack US interests in Saudi Arabia, Kenya, and elsewhere, a US official told Reuters on condition of anonymity.

"It could be a variety of potential targets. It could be a variety of types of attacks," the official said, adding that the intelligence was of roughly similar intensity to that before the bombings in Saudi Arabia earlier this week.

Coordinated suicide bomb attacks on Monday in the Saudi capital Riyadh killed 34 people in gated residential compounds that housed foreigners.

The Riyadh bombings were blamed on Saudi-born Osama bin Laden's Al Qaeda network and prompted a flurry of State Department travel warnings. These included ordering the departure on Tuesday of non-essential US embassy and consulate staff and family members in Saudi Arabia.

Earlier on Thursday, the US government cautioned against travel to Kenya, warning that 'terrorists using shoulder-fired missiles' could pose a threat to aircraft.

Britain banned flights to and from Kenya after the Kenyan Security Ministry said a senior Al Qaeda member suspected in past attacks in the east African country had been spotted in neighboring Somalia.