FEARS were growing last night that the terrorist killings in Saudi Arabia might have a knock-on effect on the global economy by sparking further rises in oil prices.

Analysts said prices could climb this week as the killing of at least 22 civilians in oil-rich Khobar raises concerns about supplies from the world's top crude exporter.

The Organisation of the Petroleum Exporting Countries (Opec) is due to meet on Thursday and all eyes will be on Saudi Arabia to see how it reacts to the situation.

The warning came as Britain's ambassador to Saudi Arabia, Sherard Cowper-Coles, warned that another terrorist attack in the country was probable.

The Foreign Office has advised against all but essential travel to Saudi, but unlike the US, it has stopped short of recommending that people leave the country.

Mr Cowper-Coles said: "The headline advice is come to Saudi Arabia only if your visit is essential. Stay here only if your presence is essential."

His comments came as reports suggested that Westerners working in the area were seeking to move to Bahrain to escape the threat of terrorist attack.

A close ally of the US, it has not seen the kind of extremist violence that has erupted repeatedly in Saudi Arabia during the past year.

Meanwhile, family members of the British oil executive shot dead at the start of the 24-hour hostage-taking incident in Khobar have flown to Saudi.

Michael Hamilton, a father-of-two, was in his car on his way to work at Arab Petroleum Investments Corp when he was gunned down on Saturday.

His wife, Penelope, who was dropped off by her husband at a nearby compound only minutes before he was shot, was said to be devastated.

She was being comforted by her two sisters and son from a previous relationship, Matthew, a lawyer in London.

Officials were investigating reports that a second Briton died in the attack, but the Foreign Office said it had no reason to believe that was the case.

An off-shoot of Osama bin Laden's al Qaida terrorist network has claimed responsibility for the outrage, which ended when Saudi commandos stormed the compound.

Three of the four attackers, who held up to 50 people hostage in the compound after attacking the offices of two oil companies, managed to flee and are being hunted.