Al Qaeda-associated militants who had been released from Saudi prisons killed two Saudi border guards while trying to cross into Yemen early on Monday before being captured, the kingdom's interior ministry said.

The militant movement's Yemeni branch, known as Al Qaeda in the Arabian Peninsula (AQAP), has several Saudis in leadership roles and has sworn to bring down the kingdom's ruling family.

Saudi Arabia has played an important role in foiling attacks planned by AQAP against international airliners, Western countries have said.

Saudi authorities have arrested thousands of suspected militants over the past decade, crushing an al Qaeda bombing campaign inside the country from 2003-06, and putting hundreds of them through a rehabilitation programme.

But several graduates of the rehabilitation programme have since emerged as leaders of AQAP in Yemen.

A ministry statement said a group of 10 Saudis and one Yemeni ambushed a Saudi border patrol just before dawn in the Sharoura sector of Najran Province, killing the two guards.

Four of the group were seriously wounded in the ambush, according to the statement issued by the Interior Ministry security spokesman and carried by the Saudi Press Agency.

It said identity papers belonging to the Saudi nationals showed they had all been previously imprisoned for crimes relating to "crimes and activities of the deviant group", as al Qaeda is officially described.

It added that they had trying to cross into Yemen, where widespread lawlessness has allowed AQAP to establish a foothold.

Earlier this year Saudi Arabia announced it had detained two al Qaeda cells in Riyadh and Jeddah that had planned bomb attacks in the kingdom.

Saudi fought a brief war on its southern border with Yemen in 2009 against the country's Houthi rebel movement, which proclaims the rights of the Shi'ite Muslim Zaydi sect there. That conflict began when Houthis ambushed a Saudi patrol, killing two soldiers.

Saudi border guards have in the past also clashed with smugglers along the long, porous desert frontier.-Reuters