By Tom Perry and Angus McDowall

BEIRUT (Reuters) – Syrian government forces bombarded eastern Ghouta anew on Wednesday in an effort to slice the rebel enclave in two as they intensified a campaign to deal the opposition its biggest defeat since 2016.

The Syrian government assault on the densely populated area on the outskirts of Damascus, which began more than two weeks ago, has become one of the fiercest campaigns of a war now entering its eighth year, with bombardment killing hundreds.

Live footage broadcast by Syrian state TV from the outskirts of the town of Mesraba showed enormous clouds of smoke rising into the sky. The sounds of explosions and jets could be heard.

A state TV correspondent said militant defenses in the town were being struck by “preparatory fire” in advance of a planned infantry assault. “Mesraba is under heavy attack today,” said Khalil Aybour, a member of an opposition council in Ghouta.

Capturing Mesraba would be a major step towards severing the northern half of the Ghouta, including its biggest town, Douma, from the southern part. Government forces have seized more than 40 percent of the territory so far.

On Wednesday pro-government forces advanced, taking the small town of Beit Sawa to Misraba’s south, a Hezbollah-run media unit said.

Civilians have been fleeing frontline areas into Douma and hiding in cellars, with aid workers saying many children had told them they had not seen daylight in 20 days. [L5N1QP5D5]

“It’s bad in the basement, but it’s better than the bombing,” Adnan, 30, a Douma resident who has been sheltering below ground with his wife and two-year-old daughter together with 10 other families, told Reuters by telephone.

The United Nations says 400,000 people are trapped in the towns and villages of the eastern Ghouta, under government siege for years and already running out of food and medicine before the assault. An aid convoy reached the area this week but government officials had stripped out most medical supplies.

The United Nations resident and humanitarian coordinator in Syria. Ali al-Za’tari, asked the government to commit to a ceasefire on Thursday to allow more aid in.

Russia, President Bashar al-Assad’s most powerful ally, has offered rebels safe passage out with their families and personal weapons. The proposal echoes previous agreements under which insurgents, in the face of military defeat, were permitted to withdraw to opposition-held areas along the Turkish border.

The Syrian Observatory for Human Rights monitoring group says at least 815 civilians have been killed by government bombing and shelling in this offensive, with 45 killed on Wednesday.

The Observatory said an extra 700 pro-government militia fighters had arrived at the front as reinforcements to join the operation.

The U.N. Security Council has called for a 30-day countrywide ceasefire, but Moscow and Damascus have not halted the campaign, arguing that the fighters they are striking are members of banned terrorist groups unprotected by the truce.

The Security Council, where Russia holds a veto, will meet on Wednesday to discuss the failed ceasefire.

Russia’s defense ministry said some rebels wanted to accept the proposal to evacuate. So far rebels have dismissed it in public. The military spokesman for one of the main eastern Ghouta rebel groups said rebels would defend the territory and there were no negotiations over a withdrawal.

“The factions of Ghouta and their fighters and its people are holding onto their land and will defend it,” Hamza Birqdar of Jaish al-Islam told Reuters in a text message sent overnight.

The opposition says such evacuation agreements amount to a policy of demographic change by which Assad has forcibly displaced those who oppose him.

In an interview on state TV, a Syrian army colonel expressed confidence Ghouta would fall quickly, saying the people there would return to the “state’s embrace … very, very, very soon”.

COMPLICITY

Russian warplanes have taken part in the eastern Ghouta operation, and the White House has accused Russia of complicity in the killing of civilians there.

Defeat in eastern Ghouta would mark the biggest setback for the anti-Assad rebellion since the opposition was driven from eastern Aleppo in late 2016 after a similar campaign of siege, bombing, ground assaults and the promise of safe passage out.

Moscow and Damascus say the Ghouta campaign is necessary to halt rebel shelling of the capital. The Observatory says such shelling has killed at least 27 people since Feb. 18.

Syrian state media have given a higher death toll and said at least five people were injured on Wednesday due to rockets falling on government-held Damascus.

A commander in the military alliance fighting in support of Assad said he anticipated rebels would end up cornered in Douma and accept a withdrawal deal.

Assad said this week that the majority of people in eastern Ghouta wanted a return of state rule. But rebels and opposition activists say people fear government persecution.

State media said some people in Ghouta raised Syrian flags. The Observatory said a few people protested in the town of Hammouriyeh calling for an end to the bombardment and for rebel groups to leave.

U.N. human rights chief Zeid Ra’ad al-Hussein said targeting a few hundred fighters was no justification for the offensive.

“Claims by the government of Syria that it is taking every measure to protect its civilian population are frankly ridiculous,” he told the U.N. Human Rights Council.

(Additional reporting by Ellen Francis, Laila Bassam and Lisa Barrington in Beirut, Maria Kiselyova in Moscow, Stephanie Nebehay in Geneva; Writing by Tom Perry; Editing by Peter Graff/Mark Heinrich)