Some three million more Syrian refugees are being "deliberately" pushed by Russia toward Europe, US diplomats have warned.

"I just want to underscore the reality and the magnitude of the challenge," David Satterfield, the US ambassador to Turkey, said in Brussels on Tuesday (10 March).

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US special envoy on Syria James Jeffrey (r) (Photo: state.gov)

"Turkey faces in the immediate case, but Europe as a whole, the challenge posed by up to three million displaced [people] moving in an increasingly compressed fashion ... up against the Turkish border," he said.

The refugees were "jammed together in about half of the province of Idlib [in northwest Syria], many of them very close to the Turkish border, who risk coming across, destabilising Turkey, and perhaps moving on to Europe," James Jeffrey, a US special envoy on Syria, also said.

The refugees were being driven out by Russian and Syrian regime forces, but Russia was in charge, the US diplomats indicated.

There was a "deliberate Russian decision to initiate a campaign in Idlib", Satterfield said.

"I underscore Russian aggression, because the Syrian regime on its own could not be conducting this campaign. This is enabled by, at all times, Russian air and ground activity, but particularly air," he said.

Russia was using the refugees as its "primary lever" in the region, he added.

"By forcing their movement, their displacement ... towards the Turkish border, Russia's calculation is this will compel Turkey to take decisions favourable to Russian ambitions," he said.

Russia's ally, the Syrian regime, also wanted the refugees, who came from rebel areas, to be cleansed, Satterfield said.

"The intent of the [Syrian] regime is to force these populations ... out of the country and to have them leave permanently. There is no prospect of refugees returning to Syria," the US ambassador said.

Syria conflict

For its part, Turkey, a Nato ally, which already hosts 3.6m refugees, is fighting in Idlib on the rebel side against the Syrian regime.

The US diplomats spoke after Turkish president Recep Tayyip Erdoğan recently opened his Greek border to migrants to draw Western attention to the situation in Syria.

Tens of thousands of people have tried to cross, prompting EU dismay.

The 2020 exodus is, so far, much smaller than in 2015, when one million people walked through Greece to Germany and further afield.

But Tuesday's US warning echoed one from 2016, when Philip Breedlove, an American general who was in charge of Nato troops in Europe, also said Russia was using refugees to destabilise the EU.

"Together, Russia and the Assad regime are deliberately weaponising migration in an attempt to overwhelm European structures and break European resolve," Breedlove said, referring to Syrian president Bashar al-Assad.

The two US diplomats spoke after Erdoğan and Russian president Vladimir Putin agreed a ceasefire on 5 March.

But Putin would break that truce sooner or later, the US warned.

"We don't believe they [Russia and Syria] have any interest in a permanent ceasefire in Idlib. They are out to get a military victory in all of Syria," Jeffrey said.

"The sad record of Syria over the course of the past two years has been ceasefires with Russian guarantees that have not been ceasefires - they were temporary, transactional halts until Russia was prepared to renew the campaign," Satterfield said.

Western sanctions

Nato and EU states were in talks on how to stop Putin in Idlib, Jeffrey added.

The US diplomats were lukewarm on Turkey's call for Nato to enforce a safe zone for refugees there.

But other options included US arms transfers to Turkey and a new "package of sanctions" designed "to encourage Russia and Syria not to do what we think they want to do, which is to break the ceasefire, push these three million refugees across the border," Jeffrey said.

"If they ignore our preparations and move forward, we will then react as rapidly as possible in consultation with our European and Nato allies," he said.

Erdoğan had strained ties with the West long before he recently reopened his Greek border.

The disputes covered Turkish human rights abuses, a Russia arms deal, and gas drilling in Cypriot waters.

But the Idlib crisis was bigger than these, Satterfield indicated.

"Turkey is a part of the Nato alliance. It is a part of Europe. It is a part, in our view, of the West," the US ambassador to Turkey said.