* Gov't cuts remaining Ghouta effectively in half -monitor
* Rebels in enclave outside Damascus will fight on -spokesman
* Russia says some rebels want to accept withdrawal deal
* UN Security Council due to discuss ceasefire Wednesday (Updates civilian death toll)
By Tom Perry and Angus McDowall
BEIRUT, March 7 (Reuters) - Syrian government forces bombarded eastern Ghouta anew on Wednesday in an effort to slice the rebel enclave in two, intensifying a campaign to deal the opposition its biggest defeat since 2016.
The Syrian Observatory for Human Rights war monitor said pro-Syrian government forces had managed to bring the strip of territory linking the north and south of what remains of rebel-held eastern Ghouta within firing range, effectively bisecting the densely populated region on the outskirts of Damascus.
There was no immediate confirmation of this from the rebels or Syrian government.
The Syrian government onslaught on eastern Ghouta, 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 of people.
Live footage broadcast by Syrian state TV from the outskirts of the town of Mesraba earlier on Wednesday showed enormous clouds of smoke rising into the sky. The sounds of explosions and jets could be heard.
A state TV correspondent said militant defences in the town were being hit 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 Ghouta, including its biggest town Douma, from the southern part. Government forces have seized more than 50 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. The Observatory said this advance deeper into the centre of the enclave enabled them to bring the remaining north-south link within firing range.
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.
"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 let in more aid.
AT LEAST 867 CIVILIANS KILLED
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 Observatory said that at least 867 civilians have been killed by government bombing and shelling in this offensive, with at least 62 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 called on Wednesday for its Feb. 24 resolution demanding a 30-day ceasefire across Syria to be implemented and it voiced concern about the country's humanitarian plight, the council president said.
Netherlands U.N. Ambassador Karel van Oosterom was speaking after the Council was briefed behind closed doors on the situation in Syria at the request of Britain and France.
Despite the ceasefire resolution, Moscow and Damascus have not halted the campaign to retake eastern Ghouta, arguing that the fighters they are striking are members of banned terrorist groups unprotected by the truce.
Russia's defence 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 that Ghouta would fall quickly, saying the people there would return to the "state's embrace ... very, very, very soon".
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 worst 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 in Damascus 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. (Additional reporting by Ellen Francis, Laila Bassam and Lisa Barrington in Beirut, Maria Kiselyova in Moscow, Stephanie Nebehay in Geneva and Michelle Nichols at the United Nations; Writing by Tom Perry Editing by Peter Graff, Mark Heinrich, Toni Reinhold)
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