Searches of the gunmen's hideout and their getaway car netted a huge cache of arms, including 55 hand grenades, 377 kilograms of explosive, and 2,545 bullets of different calibres, as well as cash and disguises, the ministry said according to Agance France-Presse (AFP).

"The security services seized a large stash of weapons, explosives and munitions in Riyadh Tuesday, May 6, which were intended to carry out acts of terrorism," said a ministry statement carried by the official SPA news agency.

The ministry said it was seeking "19 terrorists, 17 of them Saudis," but added that it expected to add other names to the wanted list later.

The two non-Saudis being sought immediately were a Yemeni and an Iraqi with joint Kuwaiti-Canadian nationality.

The ministry called on the general public to ring the nearest police station if they had any information which could lead to the suspects' arrest and warned anyone against giving them refuge.

The shootout erupted late Tuesday as police were searching for those responsible for a March 18 bomb attack which killed one person in the capital's Jazira quarter.

The gunmen's getaway car broke down but they were able to hijack another vehicle and disappear into a teeming neighbourhood.

Police discovered "55 hand grenades, 295 bullets, seven empty magazines, travel documents, identity cards and 72,957 dollars cash" in the car, AFP said.

Computers, communications equipment, travel documents, cash in U.S. dollars and Saudi riyals were found, news agencies reported.

A search of another vehicle parked in the courtyard of the house netted "three Kalashnikovs, wigs and other disguises."

An American working at a Saudi naval base was shot and injured last week prompting Washington to issue a new travel advisory warning its nationals against non-essential travel to the kingdom.

Saudi Arabia had witnessed a number of attacks and bombings in the past 5 years, targeted foreigners.

A British was killed in June 2002 after a bomb implemented in his car exploded, while 4 foreigners were killed, others injured in a blast that took place in front of a shop in Al-Khubar province, east to Riyadh.

The U.S. State Department said it had received intelligence reports indicating what the U.S. calls "terrorist" groups that may be in the final phases of planning attacks against Americans in Saudi Arabia.