Western naval forces said on Friday they feared possible attacks on oil installations in the Gulf, and Saudi Arabia said terrorist threats against the country's oil facilities were ongoing.
Oil installations in Saudi Arabia, the world's top crude producer, are a "high-probability potential target" for terrorist attack, but tight security measures are in place to protect them, said the spokesman for the Saudi interior ministry, General Mansur al-Turki.
"Coalition forces are taking prudent, precautionary measures and focusing maritime security operations in the Gulf on these possible threats," a Bahrain-based spokesman for the coalition naval forces told AFP.
Lieutenant Commander Charlie Brown said the measures were "in response to recent threats to oil infrastructure in the Gulf, including public statements by Al-Qaeda leadership".
He declined to go into details about potential targets when asked if the threats were aimed specifically against installations in Saudi Arabia, which operates the world's largest oil terminal at Ras Tannura on the Gulf.
Turki said threats to Saudi oil facilities by terrorist groups were ongoing, and that the authorities took the necessary security measures to prevent any attacks.
"The terrorist threat to industrial installations exists, and (oil facilities) are a declared target of the deviant group," Turki told AFP, using the official Saudi term for al Qaeda militants who launched a wave of attacks in the kingdom three and a half years ago.
"There are preventive measures in any installation, be it Ras Tannura or others, to prevent any terrorist operation," he said.
"Ras Tannura or any other oil installation is a high-probability potential target for terrorist threats, but I cannot confirm or deny a specific new threat" of attack against an oil facility, Turki said.
He said no "extraordinary measures" had been taken in the past few days at Saudi oil facilities, "as the (security) measures are in place, and if any information becomes available that requires stepping up or amending these measures, this is done on a routine basis".
A US State Department official, speaking anonymously, confirmed there had been a "threat" to Saudi oil installations, but could not be more specific.
Saudi Arabia announced last February that it had thwarted a bid to blow up an oil processing plant, the world's largest, at Abqaiq in the oil-rich Eastern Province.
Security forces killed the would-be suicide-bomber drivers of two vehicles laden with explosives before they could penetrate the massive complex.
Al-Qaeda, which has repeatedly threatened to target oil installations in the region, claimed responsibility for the attempted attack.
"Terrorist groups do not hesitate to threaten oil facilities... Security authorities, backed by the Saudi navy, take all adequate measures to protect all industrial and economic installations," Turki said, stressing that the measures were tight.
The Ras Tannura terminal falls along a roughly 60-kilometer (37-mile) stretch between the two main Saudi ports on the Gulf -- Dammam King Abdul Aziz port to the south and Al-Jubail industrial port to the north.
Coalition forces spokesman Brown said commercial vessels should be "especially vigilant" while transiting the Gulf.
He said that coalition naval forces, which include ships from several Western countries, "routinely conduct maritime security operations" in international waters in the Gulf, but were currently "focusing on possible threats of attacks by Al-Qaeda on oil infrastructure" in the region.
"Terrorists have demonstrated their intent to attack oil infrastructure in this region through previous attempts" such as the attack on the French super tanker Limburg off Yemen in 2002, and the attempted attacks at Abqaiq in February and in Yemen last month, he said.
Saudi Arabia pumps more than nine million barrels of oil per day and sits on a quarter of global oil reserves. World crude prices quickly firmed on Friday on news of a potential terrorist threat to oil installations in the OPEC kingpin.