ALGIERS - The Algerian army captured four heavily armed militants near the borders with Mali and Libya, a security source said on Friday, underlining international concerns that al-Qaida-linked fighters are moving across porous Saharan frontiers.

Western security experts say the lawless desert expanses of southern Algeria, Libya and northern Mali form a corridor for smugglers and Islamist militants traveling across the region.

The French and Malian army believe many al-Qaida-linked fighters in Mali have sought to cross the Algerian border after four weeks of a French offensive have driven them from Mali's northern cities.

A Malian and an Algerian man were arrested near Tinzaouatine, near the border with Mali, the Algerian security source, who asked not to be named, told Reuters.