A look at Islamic State beheadings, battle losses

As it has lost battleground in Iraq and Syria, the Islamic State group has ramped up its propaganda campaign by beheading hostages.

US officials call it a sign of weakness that shows the militants are trying to use whatever they can to maintain support and inspire recruits, even as the group suffers military setbacks in its push to create a religious empire across the two countries.

An estimated 15 to 20 hostages are still being held by the Islamic State, including two Americans.

The militants overran the northern Iraqi city of Mosul on June 8, and quickly captured a number of other cities. They were closing in on the Iraqi Kurdish capital of Irbil when the US first launched airstrikes against the Islamic State fighters Aug. 8.

A look at the timeline since then of the Islamic State group's major battlefield losses and its execution of hostages.

Aug. 8: US airstrikes begin in Iraq.

Aug. 14: Islamic State fighters are pushed from Sinjar.

Aug. 17: Kurdish and Iraqi forces retake Mosul Dam from the Islamic State group.

Aug. 19: Video released of beheading of James Foley, an American.

Aug. 23: Islamic State militants attack Syrian forces in Raqqah; group releases video of militants kicking of a severed head.

Aug. 28: Images released of Lebanese Army Sgt. Ali al-Sayyed beheaded; separately, video released of Kurdish soldier beheaded at Grand Mosque of Mosul.

Aug. 31: Iraqi and Kurdish forces retake town of Amirli.

Sept. 2: Video released of beheading of Steven Sotloff, an American.

Sept. 6: Images released of beheading of Lebanese soldier Abbas Medlej.

Sept. 7-9 US airstrikes attack Islamic State fighters at Haditha dam.

Sept. 11: British Prime Minister David Cameron says his government hasn't ruled out air power against Islamic State group in Syria.

Sept. 13: Video released of British humanitarian aid worker David Haines beheaded.

Sept. 13: Kurdish fighters advance against Islamic State militants in Syria, recapture more than a dozen villages.

Sept. 19: France joins the US in conducting airstrikes on the Islamic State group in Iraq.

Sept. 21-22: Airstrikes begin in Syria.

Sept. 24: Video released of French tourist Herve Gourdel beheaded by an Islamic State group affiliate in Algeria.

Sept. 23-Oct. 3: Islamic State fighters were bombarded by daily airstrikes in Syria or Iraq, and sometimes both.

Oct. 3: Video released of British humanitarian aid worker Alan Henning beheaded.