DUBAI (Reuters) - A top al Qaeda leader in Saudi Arabia said Osama bin Laden's group was helping Muslim militants fighting to expel U.S. forces from Iraq, according to a statement posted on Islamist Web sites on Friday.

It also claimed responsibility for a shooting this month in Saudi Arabia that killed five Westerners and vowed more deadly attacks in the world's largest oil exporter and other Muslim states.

"In our jihad in the Arabian peninsula, we are serving the Iraqi cause and helping the mujahideen there who we are in constant contact with and are supporting," said the statement attributed to Abdulaziz al-Muqrin.

"We seek to confuse the enemy, keep it occupied in its rear bases and foil its future plans along with its Arab allies and despots."

It was not immediately possible to verify the authenticity of the statement, which said Muslim militants had laid low in Kurdistan for a long time and "could not achieve what they are achieving now."

It was referring to Ansar al-Islam, a militant group which held a swathe of territory near the mountainous border between northern Iraq and Iran before being scattered by U.S. and Kurdish troops in last year's Iraq war.

The area had been beyond the control of then-president Saddam Hussein after the 1991 Gulf War, when northern Kurdish regions became autonomous.

Ansar is accused by Washington of being a Qaeda ally and a force behind attacks on U.S. troops in Iraq. Kurdish officials have alleged ties between the group and Abu Musab al-Zarqawi, whom Washington calls the leading Qaeda operative in Iraq.

Zarqawi has claimed a string of bombings and killings in Iraq, including last year's assassination of the head of the largest Iraqi Shi'ite group, Ayatollah Mohammed Baqr al-Hakim, and the bombing of the U.N. headquarters in Baghdad.

He also claimed last month's suicide attack on the Basra oil terminal and the CIA believes it was Zarqawi who beheaded U.S. civilian Nick Berg in a video shown on an Islamist Web site this week.

"We are committed to our pledge and tell everyone: blood and more blood, destruction and more destruction. You will see from us what will please and heal souls, not only in the land of Al Haramain (Saudi Arabia) but also in other Muslim states," said Muqrin.

YANBU CLAIM

The statement claimed the May 1 attack on a petrochemical site in the Saudi city of Yanbu in which four militants gunned down two Americans, two Britons and an Australian. They also dragged the body of an American through the streets.

"The Yanbu cell that carried out the successful, heroic operation this month is the best example of what is required (of militants)," it said, adding that the leader of the four had fought alongside al Qaeda in Afghanistan and Somalia.

"There was contact between us and he delivered what he promised by striking the enemy at a vital economic target, from which world oil markets have still not recovered," it said.

Muqrin, who earlier praised the shooting without directly claiming it, told militants their battles were not on the frontlines but on the streets which he said would be more difficult. He advised them to plan carefully so as not to be thwarted by security forces and to avoid killing Muslims.

"Muslims should know jihad for the sake of God in this country (Saudi Arabia) is to impose Islamic law and to expel the crusader invaders and apostates," he said, adding that militants were casing Western targets to destroy them.

Muqrin is said to have taken over leadership of al Qaeda in Saudi Arabia after the killing earlier this year of former top operative Khaled Ali Ali Haj.