(Reuters) - Algerian troops discovered a huge arms cache near the border with Libya, including hundreds of surface-to-air missiles, rockets and landmines, an Algerian security source said on Thursday. ... The source said the cache was found in Illizi in southern Algeria, about 200 km (125 miles) from the Amenas gas plant, which Libyan-based Islamist militants attacked in January, killing nearly 40 foreign contractors. The weapons included 100 anti-aircraft missiles, more than 500 MANPAD shoulder-launched rockets often used against low flying aircraft like helicopters, and hundreds of rocket launchers, rifles, landmines and rocket-propelled grenades, the source added.