The US ambassador to Saudi Arabia has urged American citizens to leave the country after five westerners were shot dead by alleged militants on Saturday.
Ambassador James Oberwetter says it is up to individuals to leave
Ambassador James Oberwetter gave the warning on a visit to Yanbu, the port city where the attack happened.
Two of those killed were Americans; US citizens employed in Yanbu's oil industry have already started leaving.
Despite the warning, Mr Oberwetter said the final decision to remain in the country rested with the individuals.
"While we are doing this urging, the US government is not in a position to cause that to happen," he told reporters.
"Those are individual decisions by private Americans and by those companies."
An American teacher told the Associated Press news agency the ambassador had effectively told US citizens, "It is time for us to pack our bags and go home... We cannot protect you here."
Chased and shot dead
Some 30,000 Americans live and work in Saudi Arabia.
Western embassies have been advising their nationals to keep a low profile in Saudi Arabia or leave, because of attacks by militants specifically targeting foreigners.
Fighters linked to or inspired by al-Qaeda have been accused of a succession of attacks against government and foreign interests in the kingdom, including the suicide-bombing of a residential compound for westerners in Riyadh in May last year, which killed 34 people.
The Yanbu attack took place at the offices of the engineering firm ABB Lummus, whose staff have since been ordered to leave the city.
A Saudi national also died in the incident and two local employees were wounded.
The attackers fled the scene with a victim of the shoot-out, whose body was fastened to the getaway car and dragged through the streets.
The authorities said they chased and shot dead the gunmen, who, they claimed, were linked to the al-Qaeda group, headed by Saudi-born fugitive Osama Bin Laden.
Ambassador Oberwetter said the Saudi government was making good progress in the battle against terrorism.
"I personally believe, because of the activities of the government of the kingdom... the climate in general will be considerably improved," he said.
Jamal Khashoggi, an adviser to the Saudi embassy in London, told the BBC the attack did not threaten the stability of the kingdom.