At least four Saudi national guards were killed by the gunmen who stormed the US consulate in the Red Sea city of Jeddah on Monday, the pan-Arab al-Jazeera TV reported.

Attackers who stormed the US consulate in Jeddah on Monday killed four Saudi guards and took 18 local staff hostage, security sources were quoted as saying.

Witnesses said Saudi security forces have broken into the compound and were chasing attackers.

A gunbattle raged inside, in the latest strike against Western targets in the kingdom, they said, adding four attackers remained inside the US consulate where a gunbattle ongoing was taking place more than an hour after the initial blast.

Earlier Monday, gunshots and explosions were heard and witnesses reported plumes of black smoke were seen rising from the area.

US Embassy spokeswoman Carol Kalin said in Riyadh that there were no reports of American casualties.

"We can confirm there has been an attack on the consulate,"Kalin said, adding "no reports of any American casualties. The incident is still in progress with Saudi emergency forces securing the compound."

It was not clear yet whether the attack was linked to Islamic militants bent on driving westerners out of the kingdom.

Violence has surged since last May, during which dozens of foreigners were attacked and several bombing attacks staged.