By Sylvie Lanteaume and Frank Zeller
Pentagon chief Patrick Shanahan struggled Friday to convince sceptical allies in the coalition fighting the Islamic State militia to help secure Syria once American soldiers pull out.
President Donald Trump said the United States will announce the end of the IS group's once-sprawling "caliphate" within 24 hours, with US-led Arab and Kurdish forces close to capturing the last IS territorial holdout in Syria.
As the end neared for the proto-state that once controlled large areas of Iraq and Syria, 13 defence ministers of the anti-IS coalition met on the sidelines of the Munich Security Conference.
Shanahan, the US acting defence secretary, pledged ongoing backing for the fight -- but kept allies guessing as to how that would be achieved once US forces pull out, and won no solid pledges of support.
"While the time for US troops on the ground in northeast Syria winds down, the United States remains committed to our coalition's cause: the permanent defeat of ISIS, both in the Middle East and beyond," he said.
Shanahan pledged that the US would "maintain our counterterrorism capabilities in the region" and "continue to support our local partners' ability to stand up to the remnants of ISIS" -- but gave no details about how this would be done.
- 'In together, out together' -
IS fighters have been boxed into an area of around one square kilometre (less than half a square mile) in a last battle over the jihadists' remaining patch of territory in northeastern Syria.
Once they are defeated, US troops are set to withdraw from Kurdish-controlled areas after Trump in December announced the pullout of around 2,000 US troops.
Belgian Foreign Minister Didier Reynders said the US had told coalition partners its soldiers would leave in "weeks rather than months".
The decision has stunned allies including France, which contributes artillery and about 1,200 forces in the region, including soldiers who train Iraqi troops.
"It is totally out of the question to have French troops on the ground without the Americans there," one French government source told AFP. "It's just no."
French Foreign Minister Jean-Yves Le Drian asked in a Munich conference panel why the US would create a vacuum in Syria that could benefit its enemy Iran, calling the approach a "mystery".
German Defence Minister Ursula von der Leyen, whose country has helped with surveillance flights and logistical support, stressed that the idea of the anti-IS mission should be "in together, out together".
A senior US defence official said that none of the allies had made any "specific commitment... either whether they would stay or (whether) they would leave when we have left".
There was "a tremendous desire to have a security arrangement or mechanism," the official said, but conceded that no concrete solution had been found to "resolve the security vacuum".
- 'Going underground' -
The imminent collapse of the IS "caliphate" in Syria has increased concerns about experienced militants and foreign fighters escaping and forming new cells in Syria or beyond.
Von der Leyen stressed that "the IS is now changing its face and is going underground and building networks, including with other terror groups and including global networks".
Shanahan said the anti-IS coalition was evolving "to meet the global threat posed by ISIS's offshoots and its murderous ideology" as far away as Afghanistan and the Philippines.
However, the key concern of US allies now is Syria, where major powers -- crucially Russia, Iran and Turkey -- are jostling for influence.
Russian President Vladimir Putin, a leading supporter of the Damascus regime, has called the expected US withdrawal "a positive step that would help stabilise the situation in this region".
Once US forces leave, another complication emerges: the future of areas in northern Syria controlled by the Kurdish YPG militia, a key US ally in the fight against jihadists but branded terrorists by Turkey.
- Observation force -
Istanbul and Washington have called for the creation of a "security zone" to separate YPG-controlled areas from the Turkish border as the US and Turkey increasingly align their positions.
Washington's suggestion of installing an observation force in a buffer zone in Syria's north has the twin objectives of avoiding a Turkish assault on Kurdish forces and halting any jihadist resurgence.
British defence minister Gavin Williamson at a NATO meeting this week did not rule out a UK role, saying that "we will continue to do all that is required to ensure that Britain and our allies remain safe".
However, one high-ranking European military official pointed to the massive challenge of creating such a security zone.
"Securing a buffer zone of an estimated 400 kilometres (250 miles) in length and 30km in width would require around 20,000 troops," said the official.