BEIRUT/AMMAN (Reuters) - The Syrian government stepped up its efforts on Thursday to retake the opposition’s last besieged enclaves, as rebels prepared to withdraw from one and a newspaper reported an ultimatum against another.

Smoke rises from Yarmouk Palestinian camp in Damascus, Syria April 19, 2018. REUTERS/Ali Hashisho

President Bashar al-Assad scored a major victory this month by retaking eastern Ghouta, the biggest rebel stronghold near Damascus, putting his forces in by far their strongest position since the early months of the seven-year-old civil war.

The United States, Britain and France launched a volley of air strikes on Saturday against three Syrian targets in retaliation for a suspected chemical weapons strike during the Ghouta assault.

The limited Western intervention, far from any contested battlefront, has shown no sign of having any impact on the ground, where Assad’s forces have pressed on with his offensive. But it showed Western powers were ready to act outside the jurisdiction of the United Nations Security Council.

The last rebels withdrew from eastern Ghouta hours after the Western bombing. Since then, the government has focused on regaining four less populous encircled enclaves.

Much of northwestern Syria is still under the control of Turkish-backed forces or militant groups, however, while a U.S-Russian de-escalation zone along the country’s southwestern borders has given some protection to Western-backed rebels.

Israel has warned it would not allow Iranian-backed militias operating alongside the Syrian army in several areas to expand their influence in that strategic border strip.

U.S. backed Kurdish-led forces are also in control of much of the area east of the Euphrates river, where Syria’s main oil and gas reserves lie.

Diplomacy this week has focused on accusations that Assad’s forces used chemical weapons use in Douma, the last town to hold out against the government advance in eastern Ghouta.

Western countries say scores of people were gassed to death in the April 7 chemical attack. Syria and its ally Russia deny that. Now the rebels have surrendered, the area is under government control, and a team of international inspectors has so far been unable to reach it.

The inspectors have delayed their visit to Douma after their security team were shot at during a reconnaissance trip on Tuesday, the Organization for the Prohibition of Chemical Weapons said.

The Western countries say Moscow and Damascus are preventing the inspectors from reaching the site and may be destroying evidence. Russia and Assad’s government deny this.

Meanwhile, the Western intervention has had so far no measurable impact on the wider war, with rebels in pockets around the capital continuing to surrender under deals that allow them to withdraw to the opposition pocket in the northwest in return for abandoning territory.

Syrian mainstream opposition leader Nasr al Hariri accused in a press conference in the Saudi capital Riyadh the Syrian government of seeking a military solution.

“The regime presses on with a military solution and continues with his military strategy without any seriousness as regards negotiations or arriving at a political settlement,” he told reporters.

SURRENDER

State television showed live footage of police and security forces entering the town of Dumayr, northeast of Damascus, where a few hours earlier buses were sent to bring out fighters and their families, while soldiers stood by the roadside.

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An estimated 5,000 people including 1,500 rebels are expected to leave to north Syria under the Russian-brokered deal that was reached earlier this week, according to opposition sources confirmed by state media.

Dumayr has been covered by an informal ceasefire for years, but its recovery is important for the government and Iranian-backed fighters with a foothold in the area as it makes it possible to guarantee the safety of vehicles traveling on the Damascus-Baghdad highway.

As well as being a major conduit for commercial trade, the highway is used by Tehran to send weapons to ally Assad. The route was suspended when Islamic State militants had partial control over Iraqi territory but has again become a key arms channel since the militants were routed last year.

Said Seif, a senior official with the Ahmad Abdo Martyrs group, said rebels had no choice but to go along with the deal to leave the town, because there were no other outside forces that could guarantee their safety.

“We hope the Russians keep their promises, even though we have no trust in them,” he said.

In the nearby enclave of Eastern Qalamoun, several towns and an area of hills which have also been covered by an informal ceasefire, rebels said they were also negotiating a withdrawal deal with Russia.

Russian military officers conducting the evacuation negotiations are pressuring rebels in Eastern Qalamoun to start negotiations to withdraw, an opposition source close to the negotiators said.

Talks also began between Russia and rebels over the fate of an enclave in central Syria around the town of Rastan where talks have centered on easing the flow of trade and passengers across crossings into government held-areas, negotiators said.

The months-long talks in northern Homs, part of broader Russian efforts to force rebels to make peace with the government, do not at this stage involve an evacuation of fighters from that rebel enclave.

Separately, the pro-government al-Watan newspaper reported on Thursday that Islamic State militants had been given 48 hours to agree to withdraw from an area around the Yarmouk camp, once Syria’s largest for Palestinian refugees, south of Damascus.

“If they refuse, the army and supporting forces are ready to launch a military operation to end the presence of the organization in the area,” al-Watan said.

Most residents have fled the camp, but thousands of civilians are still inside. Christopher Gunness, a spokesman for the United Nations Relief and Works Agency (UNRWA) which looks after the refugees said it was deeply concerned for their safety.

Referring to the latest evacuations, the United Nations said in a note it expected further displacements in the near future to northern Syria.

A commander in the regional military alliance that backs the Syrian government said the Syrian army had begun shelling the jihadist enclave on Tuesday in preparation for an assault.

Islamic State lost most of its territory last year, but it still holds small areas of desert in eastern Syria on either side of the Euphrates. On Thursday neighboring Iraq carried out air strikes against the jihadist group in Syria in coordination with Damascus, the Iraqi military said.