Zamboanga City, Philippines - Two marines were killed in an accidental grenade blast in the southern Philippines, a regional navy commander said Friday.

Commodore Alexander Pana said the accident occurred Thursday evening in the village of Comalig in Tipo-Tipo town, Basilan province, 900 kilometres south of Manila.

He said details were still sketchy on how the grenade exploded, but noted the incident was "a plain accident" and not related to the military's offensive against Muslim militants in the province.

The military has stepped up its offensive against al-Qaeda-linked Muslim Abu Sayyaf rebels in Basilan after a series of kidnappings by the guerrillas.

Troops have also been on alert against foreign Islamic militants who are reportedly training and recruiting new members in the hinterlands of the southern Philippines. (dpa)