TO GO WITH: Philippines-UN-military,FOCUS by Joel Guinto In this photo taken on September 11, 2014, Filipino peacekeeper trainees wearing anti-biological suit simulate a biological attack during a hostile environment drill at the peackeepers training center in Capas town, Tarlac province, north of Manila. To help guard the world's war zones, the Philippines plucks soldiers from the frontlines against Al-Qaeda-linked militants and communist insurgents. But battle-hardened as these 'warrior peacekeepers' are, they are also trained to turn on the charm when deployed to UN missions in Syria, Haiti and Liberia. AFP PHOTO/TED ALJIBE (Photo credit should read TED ALJIBE/AFP/Getty Images)

MANILA, Oct 2 (Reuters) - Al-Qaeda linked Islamist militants in the Philippines said on Thursday they will kill one of two German captives on Oct. 17 unless their demands are met.

Rebels from the Abu Sayyaf group captured the two Germans sailing on a yacht from the western island of Palawan island to the eastern Malaysian state of Sabah in April.

The militants are demanding a 250 million pesos ($5.6 million) ransom and for Germany to stop supporting U.S.-led air strikes against Islamic State militants in Syria.

"Today, we are going to tell you about the ultimatum," a Muslim rebel who identified himself as Abu Rami, and said he was a spokesman for Abu Sayyaf, said in a telephone call to reporters based in Zamboanga City in the south.

"After October 17, 2014, Friday, at 3 p.m., you will not see one of them alive. It will be seen by the public so that we can show that we are not playing games."

Philippine security officials say the Germans are being held in the jungles of Jolo, a remote southern island and hotbed of Islamist militants in the mainly Catholic country.

The Abu Sayyaf group has a record of kidnappings, killings and bombings. The militants are know to be holding several other foreigners.

It is not clear if the militants have contacts with Islamic State fighters in the Middle East.

Germany has ruled out taking part in air strikes against Islamic State targets in the Middle East but it did break a post-World War Two taboo on sending weapons to active conflict zones by agreeing to arm Kurdish fighters battling the militants in Iraq. (Reporting by Manuel Mogato; Editing by Robert Birsel)