By Katya Golubkova and Dahlia Nehme

MOSCOW/BEIRUT (Reuters) – The Russian military has offered Syrian rebels safe passage out of eastern Ghouta, setting out a proposal to let the opposition surrender its last major stronghold near Damascus to President Bashar al-Assad.

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 deals under which insurgents have ceded ground to Assad and been given safe passage to other opposition-held territory 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.

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 civil 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 call for a ceasefire, arguing that the rebel fighters they are targeting are members of banned terrorist groups who are not protected by the truce.

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, bombing them fiercely, 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 790 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 have encircled since 2013. Many civilian residents have fled from the frontlines into the town of Douma.

CLAIMS OF CHLORINE USE

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 area, which rebels deny.

The health directorate in rebel-held Ghouta said on Tuesday it had received reports of people suffering suffocation as a result of chlorine gas in the eastern Ghouta village of Hammourieh on Monday.

A media official with the directorate said it was “following up on the details of this incident and would release a detailed report after following up on the cases”.

Western countries and rescue workers say Syria has repeatedly used chlorine gas as a weapon in eastern Ghouta in recent weeks, which the government has strongly denied.

The civil defense rescue service in eastern Ghouta said the latest bombardment with chlorine gas had caused 30 people to suffer from suffocation in the shelling in Hammourieh.

The Syrian government swiftly denied using poison gas, and said rebels had received instructions from their foreign “sponsors” to use chemical weapons in eastern Ghouta in order to accuse the Syrian army of doing so.

The Kremlin said on Tuesday only an impartial investigation in Syria by an international commission can determine if allegations about the use of chemical weapons are true.

Asked about the possibility that the United States could strike Syria over allegations that forces loyal to Assad had used chemical weapons, spokesman Dmitry Peskov said the Kremlin hoped nothing would be done to breach international law.

Rebel-held areas of the Ghouta region were hit in a major attack with nerve gas that killed hundreds of people in 2013. Syria agreed to give up its chemical weapons arsenal to avert U.S. retaliation for that attack, but was found by the United Nations to have used sarin nerve gas again last year in an incident that prompted U.S. retaliatory air strikes.

Unlike sarin, chlorine is not banned for civilian uses, but its use as a weapon is forbidden.

Aid trucks reached eastern Ghouta on Monday for the first time since the start of the latest offensive. But the government stripped some medical supplies from the convoy and pressed on with its air and ground assault.

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.

(Reporting by Katya Golubkova in Moscow, Tom Perry and Dahlia Nehme in Beirut; Writing by Tom Perry; editing by John Stonestreet)