ZAMBOANGA, Philippines, October 19, 2009 (AFP) - Philippine authorities seized more than six tons of a chemical that is commonly used by Islamic militants to make bombs and believed smuggled in from Malaysia, the military said Monday.

The ammonium nitrate, in 242 sacks weighing 25 kilograes (55 pounds) each, was found stashed in a warehouse on the southern island of Tawi-Tawi Friday, regional military spokesman Major Ramon David Hontiveros said.

The recovery came after Marines arrested a boatman who was ferrying nine sacks of the chemicals. He then led the troops to the warehouse, where the rest of the shipment was being kept, Hontiveros said.

Hontiveros said a warehouse employee was also detained and that both men were under questioning for the illegal shipment, which is believed to have been smuggled through the country's porous southern borders.

"The said contraband was allegedly brought in from Malaysia," Hontiveros said.

Ammonium nitrate is a chemical compound commonly used as a fertilizer, although militants in the southern Philippines as well as pirates have been
known to use it in making deadly improvised bombs.

The government imposed a ban on importing the chemical in 2003 after a spate of bombings blamed on Islamic militants in the restive south using ammonium nitrate.

The Abu Sayyaf, listed by the United States as a terrorist organisation, is one of the groups that is fighting for an independent Islamic state in the southern part of this Roman Catholic nation.