Arab News quoted unnamed Yemeni security officials as saying the troops were deployed last week to assist Yemeni border guards to control the 1,800-kilometer (1,125-mile) long frontier.

"Units of the armoured corps of the army's northern sector have been deployed in the porous areas of the border with Saudi Arabia," the daily quoted the officials as saying.

The two Arab neighbours last month signed an agreement to combat inter-border arms smuggling and terrorism, following reports that explosives used in Riyadh attacks may have come from Yemen.

Large quantities of arms and explosives are smuggled every year through the border between the two nations. Hundreds of thousands of infiltrators also cross into Saudi Arabia from Yemen.

Both nations have stepped up security coordination since the September 11, 2001 attacks on the United States.

Saudi authorities in May handed over to Yemen four Yemenis suspected of being al-Qaeda members. Sanaa has also extradited to Riyadh at least 21 suspects who fled from the kingdom before and after the September 11 attacks.

WAR.WIRE