The Saudi authorities fear that Islamist radicals blamed for a series of attacks in recent years have used the porous 1,800km border to smuggle arms and explosives. In April 2005, Saudi Arabia began constructing a concrete wall along the border to prevent the smuggling of drugs including qat - a stimulant popular in Yemen.

Yemeni officials objected to the building of the wall, saying it was being erected in a demilitarised area that should remain open, according to the 2000 border agreement.