Military chiefs from 21 countries in the US-led coalition fighting the Islamic State group in Syria and Iraq will gather next week in Washington to discuss the war effort, two defense officials said Friday.

The meeting will occur against the backdrop of sobering news from the front, with IS jihadists threatening to seize control of the Syrian border town of Kobane as well as western towns in Iraq, despite a sustained campaign of air raids by US and coalition aircraft.

The US military's top ranking officer, General Martin Dempsey, "will convene a meeting of more than 20 foreign chiefs of defense next week in Washington DC to discuss the coalition efforts in the ongoing campaign against ISIL (IS group)," said a defense official, who spoke on condition of anonymity.

The extraordinary meeting will be held on Tuesday at Andrews Air Force base outside the US capital.

The four-star general overseeing the air war, General Lloyd Austin, head of US Central Command, also will be on hand to brief his fellow officers on the state of the conflict.

The gathering will include all the European partners in the coalition and all five Arab states taking an active role in the American-led air strikes against IS militants -- Bahrain, Jordan, Qatar, Saudi Arabia and the United Arab Emirates, officials told AFP.

Australia, which has sent warplanes to join the air strikes, was also expected to send its military chief, officials said.

The talks were expected to focus in part on training and arming "moderate" rebel forces in Syria and Iraqi government troops to take on the IS extremists, who have seized a large stretch of territory in Syria and Iraq.

But the gathering is also meant to carry a symbolic message, highlighting broad international support for the fight against the IS group.

The announcement came as the air war entered its third month in Iraq and its third week in Syria.

Earlier this week military officers said the coalition operation has involved nearly 5,000 sorties, including bombing raids, refueling missions and surveillance flights.