Jordan may be preparing to establish a humanitarian “buffer zone” in southern Syria using military force, a move that could bolster security along the Jordanian border and stem the flow of Syrian refugees but that would also mark the most significant violation of Syria's territorial integrity by a foreign country in four years of grinding war.

According to the Financial Times, which reported the plan on Monday, Jordan intends to carve a buffer zone into a vast area that stretches across the contested southern provinces of Deraa and Suwayda, right up along Jordan’s northern border. The zone would apparently include the city of Deraa, where a pivotal battle has been playing out in recent weeks between the government of Bashar al-Assad and rebel forces, and could include a "militarized zone" to separate the buffer area from government forces.

Jordan’s powerful, U.S.-backed military would be involved, the FT reported, but the line would be manned primarily by “existing fighters in the anti-Assad rebel southern brigades” – presumably referring to the Western-backed Free Syrian Army – and include forces currently being trained in Jordan. Few other details were immediately available.

If accurate, Monday’s report would dramatically escalate Jordan’s role in Syria and almost certainly draw accusations of invasion by Damascus and its main allies, Iran and Russia. Since the early days of Syria’s civil war in 2011, Amman has backed the so-called “moderate” rebel factions that are fighting to overthrow Assad, but it has been hesitant about intervening more overtly.

Along with Turkey, Syria’s neighbor to the north, Jordan has long called on its Western allies to help set up buffer zones, usually citing the need to relieve the enormous pressure it is shouldering as home to more than one million Syrian refugees. Amman argues that providing a relatively safe area on the Syrian side of the border – where international refugee camps could be set up and humanitarian aid could filter in – would shift the burden onto the international community and stem the flow of Syrians into impoverished, water-poor Jordan.

But analysts said the impetus for setting up a buffer zone right now could be more about burgeoning security fears. Jordan, which has kept its borders secure despite the chaos roiling Syria and Iraq, has grown increasingly anxious in recent months as the "moderate" rebel factions flounder and more radical rebel groups like the Islamic State in Iraq and the Levant (ISIL) and Al-Qaeda's Syrian franchise, the Nusra Front, creep ever closer to its borders.

"Jordan has spillover from Syria, spillover from Iraq, it’s a short distance across the Gulf of Aqaba to the Sinai Peninsula – it's just surrounded by chaos and instability," said Christopher Harmer, an analyst and Syria expert at the Institute for the Study of War. It has kept itself safe for now, but "if and when factions in Syria turn their attention to Jordan, it's an open question whether the border is defensible."

Still, Jordan’s Western allies, including the United States, have been cool on the idea of escalating involvement in Syria's messy war. They are wary that any military action beyond the current coalition airstrikes on ISIL would hasten the collapse of the Assad government and expand the power vacuum allowed ISIL to metastasize in the first place. Commenting on Monday afternoon, State Department spokesman Mark Toner said he had seen "no solid evidence" that either Jordan or Turkey were taking steps to set up a buffer zone, implying that the plan did not have Washington's blessing.

Harmer said the creation of a buffer zone could further signal that regional powers no longer believe the Assad government can realistically ever reclaim control of the country. “The moment you set up a humanitarian safe zone you’re opening the door to conversations about splitting Syria into different entities,” he said. Washington may be unlikely to back Jordan’s plan because “we’d essentially be opening the door to the dissolution of the Syrian nation-state. Of course, a lot of people say that’s already a done deal.”

According to the FT report, Jordan’s plan is backed by "key members" of the anti-ISIL coalition, though it did not name them. A spokesman for Operation Inherent Resolve, the anti-ISIL coalition of scores of countries led by the U.S. that also includes Jordan, did not comment on the report, saying only that the coalition could not discuss the matter “for operational security reasons.”