Gunmen have killed at least five Westerners in attacks in the Saudi Arabian port city of Yanbu.
The attacks occurred despite a crackdown on suspected militants
Two Americans, two Britons, at least one Australian and a Saudi national guard are among the dead.
The attackers are reported to have called themselves "mujahideen", hinting at possible links with al-Qaeda.
Local reports said one body was dragged through the streets by a car before Saudi security forces killed three of the gunmen in a shootout.
The attack began at offices just outside a petrochemical plant partly owned by the US firm Exxon-Mobil.
Saudi Arabia said the three of the gunmen worked at the site and used their entry passes to gain access, also sneaking a fourth attacker in with them.
A McDonalds hamburger restaurant was peppered with gunfire and a pipe bomb was reportedly thrown at the international school.
There was also reported to be an exchange of fire with police outside the Holiday Inn.
'Fired at random'
In a statement, the Saudi interior ministry said: "At 7am (0400GMT) on Saturday, four men entered the headquarters of a Saudi contractor in Yanbu and fired at random on Saudis and foreigners.
"Security forces chased them and they took refuge in residential areas and hijacked some cars. Three of them were killed and a fourth was wounded.
"There were a number of deaths and injuries among Saudis and foreigners."
At least four of the dead were oil engineers working for Swedish-Swiss engineering giant ABB. Another was sub-contracted to work for it.
The US embassy confirmed that two Americans had died, while the UK Foreign Office confirmed the deaths of two Britons.
A spokesman for Australian Foreign Minister Alexander Downer said an Australian national was believed to have been killed.
Local hospitals reported that 28 people, mostly Saudis, were injured.
A media adviser to the Saudi embassy in London, Jamal Kashoggi, said the gunmen had shouted, "We are the mujahideen", citing eyewitness reports.
He said this was how al-Qaeda activists in Saudi Arabia described themselves.
Saudi Arabia has seen a year-long wave of Islamist militancy, targeting mainly foreigners.
More than 50 people have been killed in suicide bombings in the capital Riyadh, including an attack on a security building last month.
But this is the first attack by anti-Western groups on an oil facility in Saudi Arabia.
The BBC's Paul Wood in Cairo says it will send shockwaves through the expatriate community and the Saudi Royal family.
Yanbu, together with Jubail, is home to much of the kingdom's oil refining and petrochemicals industries.
Earlier this month, the US urged its citizens to leave Saudi Arabia after issuing a warning of "credible indications of terrorist threats aimed at American and
Western interests in Saudi Arabia".
The Saudi ambassador to London, Prince Turki al-Faisal, said the incident would strengthen his country's resolve "to eradicate terrorist activity and to combat this evil wherever we find it".