Philippine President Benigno Aquino III vowed to crush a band of well-armed Muslim militants hiding in the jungles of the southern Philippine island of Mindanao even as he revealed the militants' foiled plots to launch terrorist bomb attacks in the capital Manila.

In a statement issued on Wednesday, Aquino also disclosed that the Abu Sayyaf appeared to have plotted to assassinate him and likewise kidnap boxing icon and lawmaker Manny Pacquiao and even his younger sister Kris Aquino, who is a famous actress and TV celebrity, the Philippine Daily Inquirer reports.

"They [militants] allegedly even hatched plots to kidnap Manny Pacquiao or one of his children, as well as my sister Kris or one of her children, with the plan to use them in bargaining for the release of their cohorts," Aquino said.

"Threats against my own life have been investigated," Aquino said, without elaborating.

Aquino said the militants wanted to bomb Manila to try to get funding from the Islamic State (ISIS). However, he said the military uncovered the plans, adding that government forces have reduced the Abu Sayyaf's ability to inflict harm.

Aquino, whose six-year term ends in June, said he will "devote all my energies" to ensure that the Abu Sayyaf would be "at the very least ... a very seriously degraded problem" for his successor.

"Casualties are to be expected. But what has to be of utmost importance is neutralising the criminal activities of the ASG," Aquino said, referring to the Abu Sayyaf militant group by a commonly used acronym.

"So, to the ASG, 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 ruled out talks with the militants who on Monday beheaded one of their foreign hostages, Canadian John Ridsdel.

The President said he had sent a letter to Ridsdel's family on Tuesday to express his condolences.

"This murder was meant to terrorise our whole population. The Abu Sayyaf thought they could instil fear in us. Instead, they have galvanised us even further to ensure justice is meted out," he said.

Aquino did not give a timeframe for the military assault.

On Wednesday, Philippine troops launched bigger, simultaneous offensives against the Abu Sayyaf in Sulu and Basilan, two island provinces in Mindanao where the terrorists are based.

In Canada, Prime Minister Justin Trudeau said he had already spoken with Aquino about possible actions against the militants who murdered Ridsdel.

The Abu Sayyaf is holding one more Canadian hostage, but Trudeau made it clear in his statement that "we will not pay a ransom."

Aquino said a sizeable Abu Sayyaf force, led by militant commander Radulan Sahiron, is surrounding the remaining hostages—Canadian Robert Hall, Norwegian Kjartan Sekkingstad and Filipino Maritess Flor.

While that is a delicate situation, "it is also an opportunity because smashing these forces is within our grasp," Aquino said.

He said the Abu Sayyaf militants have portrayed themselves as Islamic freedom fighters but "have behaved as criminals focused on enriching themselves by taking hostages for ransom."