ALGIERS, Feb 8 (Reuters) - 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 Qaeda-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 travelling across the region.
The French and Malian army believe many al Qaeda-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.
Two Libyans were also arrested in the region of In Amenas, which is near Algeria's eastern border with Libya and home to a big gas plant where a group of al Qaeda-linked militants took hundreds of people hostage last month.
"We seized two Kalashnikovs, a couple of RPG-7 missiles and some ammunition," the source said of the arrests. He said they had taken place in recent days but declined to give further details.
Thirty-seven foreigners were killed at In Amenas after Algerian troops stormed the gas complex.
The Mulathameen group, led by al Qaeda-linked Algerian jihadist Mokhtar Belmokhtar, said its raid on the plant was in response to the French-led military campaign against Islamist rebels in northern Mali.
Pro-autonomy Tuareg rebels in Mali said they detained two senior Islamist figures this week as they headed for the Algerian border.
(Reporting by Lamine Chikhi; Editing by Daniel Flynn and Pravin Char)