The Philippines army has reportedly found the remains of German hostage Jurgen Kantner who was beheaded by Abu Sayyaf militants on 26 February.

According to a military official, the 70-year-old sailing enthusiast was killed by militants – who pledged their allegiance to Isis – after their $600,000 ransom demand was not met.

Soldiers recovered both the head and the body of Kantner while carrying out a combat, search and retrieval operation in the southern province of Sulu, Colonel Crilito Sobejana was quoted by Reuters as saying.

He added that the remains would be kept in a morgue at a hospital in Sulu as documents to transport the body were being prepared.

The elderly German pleaded for help twice in two short video messages and had warned that he would be killed by the militants if ransom was not paid.

Military spokesperson Colonel Edgard Arevalo said: "The armed forces of the Philippines continues with all efforts to make good [on] its commitment to return the remains of the kidnap victim to his homeland to accord to him the decent burial he deserves."

On 28 February, Philippines President Rodrigo Duterte had apologised to Germany for not being able to save Kantner and said that the military had ramped up operations against the extremist group.

The group – known for killing individuals if ransom demands are not met – had last year killed two Canadians in a similar manner.

According to reports, they are believed to be holding at least six Filipino and 19 foreigners hostage and have raised millions of dollars from piracy and ransom payments in the past.