Police and Marines detained four residents and seized a large cache of materials for making explosives off Bongao, the provincial capital of the Tawi-Tawi island group, near the sea border with Malaysia last Sunday.
The group is suspected of supplying bomb-making equipment to Muslim guerrillas operating in Mindanao, the focus of a decades-old separatist rebellion.
De Leon said the crew of the boat where some of the materials were found had told investigators that the materials came from Malaysia.
"That’s what the detained crewmembers told us, that it included these substances for explosives manufacturing," he told reporters.
De Leon said the Navy commander in Southern Philippines is liaising with his Malaysian counterpart regarding the seized explosive materials.
Police said the Tawi-Tawi haul included more than 100 blasting caps and 146 kilograms of sodium nitrate, along with assault rifles, a pistol, computer equipment and fake Malaysian currency.
De Leon said Philippine authorities do not know from where the Moro Islamic Liberation Front (MILF) and the Abu Sayyaf are getting their weapons and explosives.
The government has blamed the MILF for a wave of bombings that hit two airports, a wharf and several public markets all over Mindanao over the past two months. The attacks have claimed dozens of lives. – AFP, Mike Frialde