MANILA: The Philippine president has apologized to Germany for failing to stop the beheading of a German hostage by Muslim militants and said a massive offensive backed by fighter jets against the extremists was underway.

Philippine officials say Jurgen Gustav Kantner was beheaded by Abu Sayyaf militants in the southern Philippines after a ransom deadline lapsed Sunday.

German Chancellor Angela Merkel condemned the killing as an "abominable act."

On Tuesday, President Rodrigo Duterte apologized and outlined the steps his government has taken to quell a wave of kidnappings by Muslim militants, including a request he made to China to help patrol the international waters bordering the southern Philippines, Malaysia and Indonesia where many piracy incidents and abductions have happened.

Duterte said China has not responded to his request.