Damascus, Aug 20 (IANS): The Islamic State (IS) group has claimed beheading a US journalist who had gone missing in Syria nearly two years ago, a media report said Wednesday.

The Sunni militant group has released a video showing one of its fighters beheading James Foley, an employee of the media company GlobalPost who was kidnapped November 22, 2012 by unidentified gunmen, Al Jazeera reported.

The IS militants said that they acted in revenge for US strikes against the group in Iraq and threatened to kill another US journalist.

"The life of this American citizen, (US President Barack) Obama, depends on your next decision," said a masked man in the video titled "A Message To America" which was posted on social media sites Tuesday.

The video could not immediately be verified.

"We have seen a video that purports to be the murder of US citizen James Foley by IS. The intelligence community is working as quickly as possible to determine its authenticity," Caitlin Hayden, a spokesperson for the US National Security Council, said Wednesday.

The IS, formerly known as the Islamic State of Iraq and Greater Syria (ISIS), established in June an "Islamic caliphate" in the territories under their control in Syria and Iraq. Since then, they have indulged in sustained persecution of non-Sunnis and other religious communities.

According to the Syrian Observatory for Human Rights, more than 6,000 rebel fighters have joined the IS in July this year.

The human rights organisation said that the IS pays a single Syrian fighter $400 a month. In case of married militants, their kids and spouses also get paid. As for fighters from overseas, they have a monthly pay of $800.