Fierce fighting to the east of Damascus has killed more than 160 people in the past two days as Syrian rebels struggle to break a months-long blockade by forces loyal to President Bashar Assad, activists said on Sunday.
It began on Friday when rebel units attacked a string of military checkpoints encircling the opposition-held suburbs in an area known as Eastern Ghouta, which has been under siege for more than six months.
Local and international aid workers say Assad's forces appeared to be trying to starve out residents - indiscriminately affecting civilians as much as rebel fighters.
The blockade has cut off rebels' weapons supplies and helped turn the tide of fighting around the capital in Assad's favor.
The battle has also drawn in hundreds of foreign fighters on both sides, underlining how Syria's civil war has stirred Sunni-Shi'ite sectarian tensions across the region.
"It is a ferocious fight between the two sides because it's a struggle over our ultimate fate here," said Bara Abdelrahman, a media activist with the rebel Islam Army brigades in the area.
The conflict in Syria has killed more than 100,000 people, according to the United Nations, and is also destabilizing Syria's neighbors.
Foreign powers are trying to bring the warring sides together for a peace conference in Switzerland before the end of the year, dubbed "Geneva 2". On Sunday, Syria's peace envoy Lakhdar Brahimi met with members of the opposition to discuss the talks, which many rebel groups have rejected without a clear guarantee that Assad will step down.
Assad's government says it welcomes talks but will not accept any preconditions.
Meanwhile, Assad's forces, emboldened by gains in central Syria in recent months, have been seizing back towns in the rebels' northern stronghold.
Rebels advance in Ghouta
The Syrian Observatory for Human Rights said rebels had advanced in Eastern Ghouta in recent fighting, seizing some small villages and the once government-held town of Deir Attiya.
Assad's forces responded with three air raids, it said.
The mainly Sunni Muslim rebels have drawn support from radical Sunni groups such as al Qaeda and other foreign militants. Shi'ite governments and militias have thrown their weight behind Assad, who is from Syria's minority Alawite sect, an offshoot of Shi'ism.
Rebels say Lebanon's Shi'ite guerrilla movement Hezbollah has joined the Eastern Ghouta battle on Assad's side, as has the Abu Fadl al-Abbas Brigade, a militia that includes Shi'ite fighters from around the Middle East.
The Britain-based Observatory, a pro-opposition group with a network of activists across Syria, said it had documented about 100 deaths on the rebel side on Friday and Saturday in Eastern Ghouta, and more than 60 among forces fighting for Assad.
But it said there were likely to be more deaths that had not been documented.
"This battle has been one of incredible human losses," said Rami Abdelrahman, head of the Observatory. "The fighting is spreading all over the eastern suburbs."
There was no comment on casualty figures from government spokesmen.
The United States, which backs the opposition, and Russia, Assad's main arms supplier, have been pushing for peace talks but a major sticking point has been the role of Shi'ite power Iran, Assad's main ally.
Opposition forces fear a deal curbing Tehran's nuclear program will lead Washington to ease pressure on Iran and Assad in Syria.
Brahimi held separate talks with Iran's foreign minister, Mohammad Javad Zarif, and Russian Foreign Minister Sergei Lavrov in Geneva in the past two days but did not meet U.S. Secretary of State John Kerry as expected.
The envoy is to host talks in Geneva on Monday between U.S. Under Secretary Wendy Sherman and Russia's deputy foreign ministers, Mikhail Bogdanov and Gennady Gatilov.
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