Analysis: Alleged beheading forces UK into war with IS group

Fawaz Gerges, Professor of Middle Eastern Politics at the London School of Economics, talks to Al Jazeera about the political and military implications of the killing of British national David Haines.

He said with the attack, the British government is "hardly pressed to join the campaign" against the Islamic State group.

He also warned that the armed rebel group would try to get as many Western hostages as possible.