Two German-speaking members of the ISIL extremist group have threatened to launch terror attacks in Germany.

The two made the threats in a five-minute execution video clip posted online on Wednesday while using assault rifles to kill two hostages in the Syrian city of Palmyra.

The two militants called on the people in Germany and Austria to either join the ranks of ISIL in Syria and Iraq or launch attacks at home.

They also vowed to take revenge for Germany’s participation in the war in Afghanistan as part of NATO military alliance and also its support for the so-called international coalition against ISIL.

The footage comes as Berlin’s estimate shows 600 Germans have so far joined Takfiri militant groups operating in Syria and Iraq.

According to a report by the United Nations, over 25,000 militants from more than 100 nations have become part of al-Qaeda and ISIL Takfiri militants in Iraq, Syria and other countries.

The analysis, which was carried out by a panel of experts monitoring UN sanctions against al-Qaeda, shows that the number of foreign terrorists spiked by 71 percent between mid-2014 and March 2015, the Associated Press reported on April 1.

Syria and Iraq have been the destination for over 20,000 of the militants, where they went to join ISIL and the al-Nusra front, the report added.

The Takfiri extremists currently control parts of Syria and Iraq. They have carried out atrocious crimes in the two countries, including mass executions and the beheading of people.

Security officials in Western states fear that those who have joined the terrorist groups in the Middle East will use their combat skills against their homelands upon returning.