MANILA — Fifteen Philippine soldiers have been killed this week and 12 others wounded in mounting clashes with the militant group Abu Sayyaf, the military said Tuesday, as the government revealed plans to deploy thousands more soldiers to the group’s southern stronghold.

It said a “series of clashes’’ had begun Monday, as the troops scoured jungle terrain on the southern island of Jolo in search of rebel fighters and at least 23 hostages, including a Dutch bird-watcher kidnapped in 2012 and a Norwegian abducted last year from a resort he helped manage.

A spokesman for President Rodrigo Duterte said Tuesday that the deaths had only strengthened the government’s resolve to crush Abu Sayyaf, which was founded in the early 1990s to fight for an independent Islamic state in the southern Philippines but which in more recent years has degenerated into a kidnap-for-ransom gang known to behead captives.

The president had approved the deployment of about 2,500 more soldiers, or five battalions, to Jolo to augment the forces there.

A report by the military said heavy fighting broke out Monday afternoon when army troops came upon 30 heavily armed Abu Sayyaf fighters on the outskirts of the remote town of Patikul on Jolo, which is part of Sulu province. A half-hour gun battle left two gunmen dead, the report said.

Later that day, a scout ranger battalion briefly encountered about 80 Abu Sayyaf fighters. The gunmen then apparently called in reinforcements, and a third clash erupted, the military said.

New York Times