Police have conducted raids throughout the kingdom

A senior government adviser said recent attacks showed terrorists were trying to damage the industry by scaring away foreign workers.

Adel al-Jubeir said militants' aim was to undermine the economy and bring down the Saudi government, but said such a strategy would not succeed.

His comments come days after attacks in Khobar left 22 people dead.

We are determined to crush this evil and go after those who finance it Adel Jubeir

On Wednesday, Saudi security forces killed two suspected militants said to be linked to the weekend attacks on an oil workers' compound in the city.

The men were hunted down in the remote Hada region of Taif in the west.

But speaking during a visit to Washington, Mr Jubeir said: "The oil installations are very, very secure."

He added that fewer than 10% of Saudi oil employees were foreigners.

Mr Jubeir also said there would be tighter controls over the movement of charitable funds abroad.

The al-Haramain Islamic Foundation, which is suspected of aiding al-Qaeda, and other private charities will be dissolved or have their assets taken over by a new national charitable commission, he said.

"We are determined to crush this evil and go after those who finance it," Mr Jubeir said.

Attack fears

BBC security correspondent Frank Gardner, in Khobar, says Western expatriates there are bracing themselves for the possibility of more terrorist attacks on their housing compounds.

It is now clear there are several units of al-Qaeda militants at large in the country, with no clues as to where they will strike next, our correspondent says.

The official American advice remains for US citizens to leave the kingdom while Britain says travel to Saudi Arabia is to be avoided if at all possible, predicting that more attacks are on the way.

Crude oil prices have surged to record prices as the Khobar attack stoked fears of turmoil in the world's largest exporter.

Representatives of the oil exporters cartel Opec are gathering in the Lebanese capital Beirut for discussions on how to cool the market.

Riyadh shooting

It is not clear how the men killed on Wednesday in Taif were linked to the carnage in Khobar, but Saudi-owned television station al-Arabiya said the pair were al-Qaeda gunmen.

Guns and ammunition were found on their bodies and one of them was disguised as a woman, al-Arabiya reported.

In a separate incident in the capital Riyadh, two cars carrying US military training personnel were shot at.

One driver was slightly hurt in the Riyadh shooting, when attackers hiding behind a row of parked cars opened fire on two vehicles coming out of the Eskan training base.

The vehicles belonged to US military advisers working with the Saudi National Guard, who sped back into the base after the attack. The gunmen escaped.

Khobar questions

Three militants were reported to have slipped through a security cordon after the Khobar attack which ended on Sunday.

A massive manhunt is under way, as more details emerged about how they had escaped a siege by large numbers of security forces.

A security adviser to the Saudi royal family, Nawaf Obaid, said the Saudi authorities had been fooled into believing that accomplices would blow up the entire housing compound where the militants were holding dozens of hostages.

The attackers had already killed 22 people with guns and knives, most of them foreigners whom the attackers had identified as non-Muslims.