Philippine military officials say at least 18 soldiers have been killed in fierce daylong fighting with Muslim militants in the south.

Three military officials told The Associated Press that at least 52 other soldiers were wounded in the clashes with Abu Sayyaf militants and allied gunmen Saturday on Basilan island.

The three senior officials spoke on condition of anonymity because they were not allowed to publicly discuss details of the clashes.

It's the largest single-day combat loss by government forces this year in the south, where the military has been battling Muslim separatist rebels and extremists and Marxist guerrillas.

The large combat losses were reported as the country marked the Day of Valor to remember Filipino veterans who perished in the last world war.