The Philippine military came under increased pressure on Tuesday to rescue more than 20 foreign hostages after their Muslim extremist captors beheaded a Canadian man, but troops face a dilemma in how to succeed and also ensure the safety of the remaining captives.

Abu Sayyaf gunmen beheaded John Ridsdel on Monday in the southern densely forested province of Sulu, sparking condemnations and prompting Canadian Prime Minister Justin Trudeau to pledge to help the Philippines pursue the extremists behind the "heinous act".

Ridsdel's head, which was placed in a plastic bag, was dumped by motorcycle-riding militants on Monday night in Jolo town in impoverished Sulu, about 950 kilometers south of Manila, where the Abu Sayyaf and allied gunmen are believed to be holding 22 foreign hostages from six countries.