Here is a chronology of the main developments that have shaped an international coalition against the Islamic State group in Syria and Iraq, where US air strikes began two months ago.

- June 9, 2014: Sunni jihadists from the Islamic State of Iraq and the Levant launch a lightning offensive in northwestern Iraq and seize the second biggest city Mosul before sweeping across much of the Sunni Arab heartland.

- August 8: US jets strike IS positions in northern Iraq, the first American military operation in the country since troops withdrew in late 2011. A week later, the European Union authorises the delivery of arms to Iraq's Kurds.

- August 17: Kurdish fighters retake Mosul dam, the biggest in Iraq, with help from US strikes.

- August 19: IS says it has beheaded US journalist James Foley, who was seized in northern Syria in 2012, releasing a video of the incident.

Similar beheadings then take the lives of US journalist Steven Sotloff on September 2, and British aid workers David Haines on September 14 and Alan Henning on October 3.

French alpinist Herve Gourdel is killed the same way in Algeria on September 24 by a group allied with the IS.

- September 5: At a NATO summit in Wales, US President Barack Obama vows to build "a broad, international coalition" to defeat IS.

- September 10: Obama says he is ready to target the IS with air strikes "wherever they exist" in a sign he plans to attack the jihadists inside Syria.

- September 16: IS launches an offensive in northern Syria that drives 300,000 people from their homes, of which 180,000 flee to Turkey.

- September 19: French jets carry out their first air strikes against IS in Iraq.

- September 21: IS forces lay siege to the Syrian Kurdish town of Kobane to seal control over a large band along the border with Turkey.

- September 22: IS calls on Muslims to kill citizens of countries that have joined the coalition, in particular US nationals and the "filthy French".

- September 23: The US and Arab allies -- Bahrain, Jordan, Saudi Arabia, Qatar and the United Arab Emirates -- launch strikes on IS militants in Syria.

- September 25: In Syria, the coalition strikes target oil installations to deprive IS of revenues.

At the United Nations, Iran deplores "strategic blunders of the West in the Middle East."

- September 30: A Kurdish counter-offensive gets underway in northern Iraq.

- October 2: The Turkish parliament approves joining the coalition, 12 days after IS releases 46 Turkish hostages.

- October 3: Britain carries out its first strikes in Iraq. Australia, Belgium, Denmark and the Netherlands also pledge combat assets.

The Iraqi army, backed by Sunni tribesmen and Shiite militia fighters, retakes the town of Dhuluiyah, north of Baghdad.

- October 6: In Syria, IS fighters penetrate the town of Kobane, which Kurds say cannot be protected by coalition air strikes alone.

In Iraq, the army struggles to advance against IS fighters and the US commits vulnerable combat helicopters to the battle.

- October 7: The US army acknowledges that of the roughly 2,000 air strikes made since August 8 in Iraq and Syria, only 10 percent were carried out by its coalition partners.