MANILA (Reuters) - Philippine President Benigno Aquino, reacting publicly for the first time to the beheading of a Canadian hostage by Islamic Abu Sayyaf militants, vowed on Wednesday to devote all his energy to eliminating the group before he steps down in two months.

Philippine President Benigno Aquino arrives at a session of the 27th Association of Southeast Asian Nations (ASEAN) Summit in Kuala Lumpur, Malaysia in this November 21, 2015 file photo. REUTERS/Olivia Harris

John Ridsdel, 68, a former mining executive, was executed on Monday by Abu Sayyaf who captured him and three others in 2015 while they were on vacation on a Philippine island.

Canadian Prime Minister Justin Trudeau condemned the execution as “cold-blooded murder”.

Security is precarious in the southern Philippines, despite a 2014 peace pact between the government and the largest Muslim rebel group that ended 45 years of conflict.

“So, to the ASG (Abu Sayyaf Group), and whoever may aid or abet them, you have chosen only the language of force, and we will speak to you only in that language,” Aquino said in a statement.

“Casualties are to be expected. But what has to be of utmost importance is neutralising the criminal activities of the ASG.”

The Philippine army said a severed head had been found on a remote island on Monday, five hours after the expiry of a ransom deadline set by the militants, who had threatened to execute one of four captives. Police confirmed the head to be that of Ridsdel.

On Wednesday, army spokesman Major Filemon Tan said a headless body was found in a dried creek, near jungle where Ridsdel was believed to have been beheaded.

“We are still verifying if the body is that of John Ridsdel,” Tan told reporters.

Abu Sayyaf is a small but brutal militant group known for beheading, kidnapping, bombing and extortion in the south of the mainly Catholic country.

Ridsdel and three others, including a Norwegian and another Canadian, were abducted seven months ago in the southern Philippines and appealed in a March video for their families and governments to secure their release.

Other foreigners held by Abu Sayyaf include one from the Netherlands, one from Japan, four Malaysians and 14 Indonesians.

Canada and Britain will urge other nations not to pay ransoms to free kidnap victims, Trudeau said on Tuesday, the day after a Canadian hostage was found dead in the Philippines.