Saudi King Abdullah, in a Ramadan message on Saturday, vowed to crush Islamist militants threatening the kingdom, the state news agency reported, saying the world's top oil exporter would not tolerate "a band of terrorists".

The remarks came two days after the monarch ordered all necessary measures to protect the country against potential "terrorist threats" resulting from turmoil in neighbouring Iraq, where Sunni Islamist militants have captured some cities from the government of Shi'ite Prime Minister Nouri al-Maliki.

"We will not let a band of terrorists who have taken religion as a disguise behind which they hide private interests to terrorise the protected Muslims, to touch our homeland or any of its sons or its protected residents," King Abdullah said in a message at the start of the  Ramadan.

Saudi Arabia crushed al Qaeda after the Islamist militant group began a campaign of bombings and attacks on vital installations and expatriate compounds in the kingdom.

The US-allied kingdom has been rattled by a lightning advance through Iraq by Sunni militants spearheaded by the Islamic State in Iraq and the Levant (ISIL) - aided by other Sunni militants, tribal leaders and remnants of Saddam Hussein's Baath Party - which seized swathes of the country this month.

Saudi Arabia shares an 800-km border with Iraq.-Reuters