Foreign ministers of the major powers, including both Washington and Moscow, ended a meeting of the International Syria Support Group (ISSG) in Vienna with no proposal for a date to resume peace talks between the Syrian government and the collection of Western-backed Islamist militias that constitute the “armed opposition.”

The so-called rebels walked out of the last round of talks in Geneva, accusing government forces of continuing to attack their positions in violation of a February 27 cessation of hostilities brokered by the US and Russia.

The government of President Bashar al-Assad and its allies, Russia and Iran, have insisted that continued operations were being carried out against the Islamic State of Iraq and Syria (ISIS) and the Al Nusra Front, Syria’s Al Qaeda affiliate, both of which are designated by the United Nations Security Council as terrorist groups and remain excluded from the shaky cease-fire.

In a communiqué issued at the close of the Vienna meeting, the ISSG member states warned that the consequences of a failure to fully implement the cessation of hostilities “could include the return of full-scale war.”

While the communiqué warned of consequences for any party violating the agreement, including “the exclusion of such parties from the arrangements of the cessation and the protection it affords them,” it gave no indications of what concrete actions would ensue.

What is painfully obvious, however, is that alleged violations by forces loyal to the government of Assad could provoke retaliation from the US, whose warplanes are already engaged in strikes on ISIS targets in Syria. At least 250 Special Operations troops have also been deployed on the ground, without the permission of Damascus and in violation of international law.

A US air strike against the city of al-Bukamal in Dayr al-Zawr province near Syria’s border with Iraq reportedly killed three children and one woman on Monday.

Violations by the so-called rebels, meanwhile, are ignored by their Western sponsors, and would be punished only by the government and its ally, Russia.

This is clearly a formula for an intensification of a conflict that has already claimed over a quarter of a million lives, while driving some 11 million Syrians from their homes. It also creates the conditions for the Syrian conflict to spill over into a wider war pitting the US against Russia.

Washington only entered into the Syrian “peace process” as a means of buying time under conditions in which Russia’s intervention on the side of the Assad government had reversed the tide of battle against the Western-backed Islamist militias and thrown the US-orchestrated war for regime change into disarray.

From the outset, the Obama administration has threatened to resort to a “Plan B” if the negotiations in Vienna and Geneva fail to achieve Washington’s original aim in stoking the bloody war in Syria: the toppling of the Assad government and the imposition of a more pliant Western puppet regime. Last month, unnamed senior US officials let it be known that “Plan B” would include the provision of more sophisticated weaponry to the “rebels,” including MANPADS, portable shoulder-fired missiles that could bring down Russian planes.

Secretary of State John Kerry, speaking to the media alongside Russian Foreign Minister Sergei Lavrov and UN special envoy Steffan de Mistura at the close of the Vienna conference, issued a direct threat to Syria’s Assad, stating, “He should never make a miscalculation about President Obama’s determination to do what is right at any given moment of time where he believes he has to make that decision.”

For his part, Lavrov charged that Washington’s key regional allies, including Turkey, are pouring more arms into Syria to fuel the conflict. Lately, he said, this has included the provision of tanks to the “rebels.”

The “main supply conduit for extremists,” the Russian foreign minister said, is a 90 kilometer stretch of the Turkish-Syrian border controlled on one side by the Turkish military and, on the other, by ISIS. He charged that there existed “a large, widely-spread network created by Turkey on its side of the border to continue and cover up these supplies.”

Kerry spent the weekend preceding the Vienna talks in Riyadh, meeting behind closed doors with representatives of the Saudi monarchy, a principal US regional ally and main supporter of the Islamist forces in Syria. The Saudi regime was the organizer of the so-called High Negotiations Committee, which was formed to represent these Salafist jihadi militias in talks with the Syrian government.

Speaking at the conference in Vienna, Saudi Foreign Minister Adel al-Jubeir advocated a speedy escalation of the war for regime change in Syria.

“We believe we should have moved to a ‘Plan B’ a long time ago,” Adel al-Jubeir told reporters. “The choice about moving to an alternative plan, the choice about intensifying the military support [to the opposition] is entirely with the Bashar regime … He will be removed, either through a political process or through military force.”

Meanwhile, Turkey, Washington’s NATO ally and also a key backer of the “rebels,” threatened Tuesday to carry out a unilateral military intervention in Syria.

President Tayyip Erdogan told a meeting in Istanbul that the Turkish military would act alone, supposedly to deal with ISIS missile attacks coming across the Syrian border and striking the town of Kilis.

“We will solve that issue ourselves if we don’t receive help to prevent those rockets from hitting Kilis,” he said. “We knocked on all doors for a safe zone at our southern border. But no one wants to take that step.”

Erdogan’s statement echoed that made by Turkish Prime Minister Ahmet Davutoglu earlier this month: “If necessary, Turkey may launch a ground military operation in Syria by itself.”

Erdogan’s remarks made clear that his concern is not ISIS, which Ankara has armed and supplied, but rather the growing strength of Syrian Kurdish forces near the Turkish border. In a thinly veiled criticism of US backing for these forces, he declared: “States which exercise control over the world’s arms industry give their weapons to terrorists. I challenge them to deny this.”

The Turkish government is committed to the war for regime change in Syria and has demonstrated, with its shoot-down of a Russian jet last November, its willingness to push this conflict into an armed confrontation with Moscow.

There is little doubt that the Saudi and Turkish regimes are openly advocating a policy that is being supported within powerful sections of the US ruling establishment and military and intelligence apparatus.

An escalation of the Syrian bloodbath also has the backing of the leading candidates in both the Democratic and Republican parties, but its initiation is almost certain to be postponed until after November in order to prevent the subject of war becoming an issue in the US presidential election.