MOSCOW/BEIRUT (Reuters) - The Russian military has offered Syrian rebels safe passage out of eastern Ghouta, setting out a proposal to let the insurgents surrender their last major stronghold near Damascus to President Bashar al-Assad, which fighters have so far rejected.

A man pushes a cart past damaged buildings at the besieged town of Douma, Eastern Ghouta, Damascus, Syria March 5, 2018. REUTERS/Bassam Khabieh

The Russian defense ministry said rebels could leave with their families and personal weapons through a secure corridor out of eastern Ghouta, where Moscow-backed government forces have made rapid gains in a fierce assault.

The Russian proposal did not specify where the rebels would go, but the terms echo previous evacuation deals under which insurgents have ceded ground to Assad and departed to opposition-held territory in the north near the Turkish border.

“The Russian Reconciliation Centre guarantees the immunity of all rebel fighters who take the decision to leave eastern Ghouta with personal weapons and together with their families,” said the defense ministry statement. Vehicles would “be provided, and the entire route will be guarded”, it added.

United Nations Secretary-General Antonio Guterres, in a statement issued by a spokesman on Tuesday, voiced concern about attacks in eastern Ghouta which “reportedly claimed the lives of more than 100 people” on Monday, as well as reports of shelling of Damascus.

Hundreds of civilians have been killed in the besieged enclave of satellite towns and rural areas on the outskirts of Damascus in one of the fiercest bombing campaigns of the seven-year-old war.

The United Nations believes 400,000 people are trapped inside the enclave where food and medical supplies were already running out before the assault began with intense air strikes two weeks ago.

Damascus and Moscow have pressed on with the campaign despite a U.N. Security Council demand for a ceasefire, arguing that the rebel fighters they are targeting are members of banned terrorist groups who are unprotected by the truce. The Security Council will meet on Wednesday to discuss the failed ceasefire.

The offensive appears to have followed the tactics Assad and his allies have used at other key points in the war: laying siege to rebel-held areas, subjecting them to bombardment, launching a ground assault and offering passage out to civilians who flee and fighters who withdraw.

Wael Alwan, the spokesman for one of the main rebel groups in eastern Ghouta, Failaq al-Rahman, said Russia was “insisting on military escalation and imposing forced displacement” on the people of eastern Ghouta, which he called “a crime”.

Alwan, who is based in Istanbul, also told Reuters there had been no contact with Russia about the proposal.

The Syrian army has captured more than a third of the enclave in recent days, threatening to slice it in two. The Syrian Observatory for Human Rights war monitor says government bombardment of the area has killed 800 people since Feb. 18, including 80 people killed on Monday alone.

Assad said on Sunday the Syrian army would continue the push into eastern Ghouta, which government forces and allied militia have encircled since 2013. On Tuesday, Syria’s SANA state news agency said troops captured the village of Muhamadiya at the edge of the enclave.

PLANE CRASHES

A Russian military transport plane crashed in Syria on Tuesday, killing all 39 people on board, Russian news agencies quoted the defense ministry as saying, sharply raising the death toll from the Kremlin’s intervention in the Syrian war. Initial information suggested a technical fault may have been to blame, the ministry was cited as saying.

The Kremlin said President Vladimir Putin expressed his condolences to the families and colleagues of the dead.

Hundreds of thousands of people have died and more than 11 million have been made homeless by the Syrian conflict, which has drawn in neighbors and global powers.

A report by U.N. war crimes investigators covering the six months until Jan. 15 said both Russia and the United States had been responsible for large-scale killings of civilians in air strikes. Russian forces had killed at least 84 civilians in an air strike in November near Aleppo, while a U.S.-led coalition fighting against Islamic State had bombed a school in March 2017, killing around 150 displaced people sheltering there.

The report also found that Syrian government forces had used chemical weapons. It called for war crimes to be punished.

For the rebels fighting to oust Assad, the loss of eastern Ghouta would mark their worst defeat since the battle of Aleppo in late 2016. Rebel shelling on Damascus has killed dozens of people during the last two weeks, state-run media has said.

Russia has organized daily, five-hour long “humanitarian ceasefires” with the stated aim of allowing civilians to leave and to permit aid deliveries. It has accused rebels of preventing people from leaving the enclave, which rebels deny.

Aid trucks reached eastern Ghouta on Monday for the first time since the start of the latest offensive. But the government had stripped some medical supplies from the convoy.

The convoy of more than 40 trucks pulled out of Douma in darkness after shelling on the town, without fully unloading supplies during a nine-hour stay. All staff were safe and heading back to the capital Damascus, aid officials said.

Guterres said nearly half of the food could not be delivered, the U.N. statement said, and he called on all parties to allow the delivery of medical and other supplies for 70,000 people in Douma planned for Thursday, as agreed with Syrian authorities, the U.N. statement added.

The health directorate in rebel-held Ghouta said on Tuesday it had received reports of people suffering from breathing problems in the Ghouta village of Hammourieh on Monday.

A missile hit a basement and released an irritating substance that led to mild symptoms, including coughing, red eyes, and sore throats among 29 people, it said.

The Syrian foreign ministry dismissed reports of a suspected gas attack as lies, state media said.

Western countries and local rescue workers have accused the Syria government of gas attacks in eastern Ghouta, which the government has strongly denied.