A western engineering firm said on Sunday it was evacuating all 90 foreign staff from the Saudi city of Yanbu after gunmen shot dead five of their colleagues on Saturday.
ABB Lummus said all 90 of its expatriate staff and around 30 dependents were being evacuated from Yanbu.
"Given the choice of staying under tighter security or leaving, they opted for leaving," spokesman Bjorn Edlund said.
Other expatriates in the city said it was too soon to decide. "It's been a shock," said one. "There's been no panic but everyone is concerned and they will have to decide what steps to take." The US embassy urged Americans to leave the kingdom.
US government advice was unambiguous. "Last night we sent a message to all Americans," an embassy spokeswoman said. "Our advice stands. Americans should not travel to Saudi Arabia and those that are here should depart."
There was no immediate indication if the latest attack would prompt an exodus among the 35,000 Americans - a move that could badly damage the economy of the world's biggest oil exporter.