According to Lebanese media, "Islamic State" (IS) militants have decapitated a Lebanese soldier.

Twenty-year-old Abbas Medlej, a Muslim Shiite, was kidnapped by the terrorist group in northeastern Lebanon in August.

Lebanese authorities were still verifying the veracity of the photographs, which were posted online on Saturday.

Syrian Civil War spills over

In a video message from the end of August, the IS had threatened to kill nine Lebanese soldiers unless the government released Islamist detainees.

Around two dozen more Lebanese soldiers have been held captive since August 2, when Syrian rebel factions, including IS militants, overran the town of Arsal and killed and kidnapped police.

The town borders Syria and has a Muslim Sunni majority which supports the Syrian opposition rebels in their fight against Syrian President Bashar al-Assad.

On Saturday, Lebanon state-run news agency said there was heavy fighting in the barren hills between Arsal and the border with Syria.

Violence reigns in the caliphate

IS seeks to impose its ultra-conservative and violent interpretation of Islam on the "caliphate" which it seeks to set up in much of the Middle East. The group has become synonymous with mass killings and torture and has decapitated a number of victims and has already taken over large swathes of Syria and Iraq.

The militant group released a video last Tuesday showing the beheading of 31-year-old US journalist Steven Sotloff, two weeks after they decapitated US journalist James Foley. Over the past two weeks, the group also released videos of the decapitation of another Lebanese soldier and Kurdish Peshmerga fighter.

Matthew Olsen, director of the US National Counterterrorism Center, said the IS could soon become the world's most dangerous terrorist organization. The group could become an even greater threat than al Qaeda, which was responsible for the September 11, 2001 terrorist attacks in the United States. The IS is well equipped financially: currently, the group takes in more than a million dollars a day, from sources including ransoms for hostages, and has a sophisticated recruitment program for would-be terrorists who are flocking to the region.

Last week, the United Nations Human Rights Council said it would open an investigation into war crimes committed by IS militants in Iraq. The evidence could be used as part of any international war crimes prosecution.

sb/av (dpa, AP)