By Hader Glang

ZAMBOANGA CITY, the Philippines

Philippine authorities blamed a Daesh-affiliated group Tuesday for an ambush that killed at least two military intelligence operatives in the troubled southern island province of Sulu.

Brig. Gen. Alan Arrojado, Joint Task Group Sulu commander, said the soldiers were returning to the 10th Infantry Battalion headquarters when they were attacked in Patikul town, an Abu Sayyaf stronghold.

He added in a text message that the two intelligence operatives “died on the spot”, and a pursuit operation has been lunched.

Authorities have tagged a group led by Abu Sayyaf sub-leader Morasil Mudjahirind as behind the ambush.

The incident occurred amid military operations aimed at gathering intelligence on the whereabouts of four hostages -- three of them foreigners -- who suspected Abu Sayyaf members threatened to execute in a recently released video.

The video uploaded on Facebook last week showed Canadians John Ridsdel and Robert Hall and Norwegian Kjartan Sekkingstad shirtless and surrounded by armed men, who Hall identified as the Abu Sayyaf.

The three thin, bearded and handcuffed men -- who were kidnapped alongside a Filipina from a resort in Davao del Norte province in September -- appeal to their governments for help securing their release, saying that if their kidnapper's demands are not met they will be killed.

Sekkingstad added that they are being held hostage on Sulu.

In an earlier video, the kidnappers had demanded P1 billion pesos ($21,500) for each of the three foreigners.

The military cautioned Monday that the video clip was "misleading", and the captors may have ordered the hostages to say they were in Sulu to deceive security forces.

"They are just misleading our troops because of continuing operations in Sulu," Maj. Filemon Tan, Western Mindanao Command spokesperson, said in a text message.

"They [Abu Sayyaf] could be using the video to tell us they are in Sulu province when they are, like for example, in Basilan province."

Military cyber forensic experts are set to investigate the video to determine when and where it was filmed, as well as who uploaded it on the Internet.

The Abu Sayyaf -- which has reportedly pledged allegiance to Daesh -- is also holding a Dutch man kidnapped more than three years ago in Tawi-Tawi and a former Italian priest seized last year in Zamboanga del Norte.

Since 1991, the group -- armed with mostly improvised explosive devices, mortars and automatic rifles -- has carried out bombings, kidnappings, assassinations and extortions in a self-determined fight for an independent Islamic province in the Philippines.

It is notorious for beheading victims after ransoms have failed to be paid for their release.