Fighting since late last year has displaced more than 240,000 people in the wider Raqqa province even as some 50,000 people still remain trapped in Daesh-controlled areas, officials say.
Scores of civilians are fleeing Syria's Raqqa traumatised, with families torn apart and conditions worsening as the battle to oust Daesh intensifies, a senior UN official said on Thursday.
The number of people escaping has risen rapidly in recent weeks, Sajjad Malik, the UN refugee agency's representative in Syria, said.
"They're coming out really weak, thirsty, and frightened," he said, after visiting several camps for the displaced in northeast Syria.
The US-backed YPG is a leading part of the Syrian Democratic Forces (SDF), which launched an operation earlier this month to capture Raqqa, Daesh's de facto Syrian capital.
Turkey considers the YPG to be a terrorist group due to its affiliations with the PKK, which launched an insurgency against the Turkish state four decades ago.
With air strikes and special forces from the US-led coalition, the SDF pushed into Raqqa in June after advancing on the city for months.
Fighting since late last year has displaced more than 240,000 people in the wider Raqqa province, most of them only in the last few weeks, Malik said.
"Dead bodies rotting in heat"
"(There are) dead bodies all over the place. In some more destroyed neighbourhoods, bodies are still in that heat rotting on the street and in debris."
An estimated 30,000-50,000 people remain trapped in the city with Daesh holding people there against their will, Malik said. Witnesses say the militants have shot at those trying to escape.
The US-led coalition says that it goes to great lengths to avoid civilian casualties.
However, ahead of the attack on the city, the UN human rights office raised concerns about increasing reports of civilian deaths. In a May report, it said there had been "massive civilian casualties ... and serious infrastructure destruction."
Rights groups like Syrian Network for Human Rights , Syrian Observatory for Human Rights, Amnesty International and London-based NGO Airwars have separately reported massive civilian deaths in coalition strikes in both Raqqa and Mosul city in Iraq.
Daesh militants still control swathes of Syria's eastern desert bordering Iraq and most of Deir al-Zor, which would be its last major foothold in Syria after losing Raqqa.
Russia willing to monitor ceasefire
Russia has said it is willing to deploy monitors to prevent any violations of a ceasefire in southwestern Syria by Syrian regime forces, a senior US official said on Thursday.
Brett McGurk, US special envoy for the coalition against Daesh, said the United States was "very encouraged" by the progress since the ceasefire arranged by the United States, Russia and Jordan took effect on Sunday.
"The Russians have made clear they're very serious about this and willing to put some of their people on the ground to help monitor from the regime side," McGurk said.
Russia is the main backer of Syrian regime leader Bashar al Assad, and Russian air power and Iranian-backed militias have helped put mostly Sunni rebels at a disadvantage over the past year.
Trump hails talks with Putin
US President Donald Trump said on Thursday that a ceasefire in southern Syria showed that his talks with Russian counterpart Vladimir Putin last weekend had produced results.
"By having (a) dialogue we were able to have a ceasefire. It's going to go on for a while and frankly we're working on a second ceasefire in a very rough part of Syria," Trump said.
"And if we get that and a few more, all of a sudden you're going to have no bullets being fired in Syria. And that would be a wonderful thing."
French President Emmanuel Macron said on Thursday that he and Trump had asked diplomats to draw up a concrete initiative aimed at preparing for the future of Syria in the coming weeks.
"On the Iraq-Syria situation, we have agreed to continue working together, in particular on the building of a roadmap for the post-war period," Macron said in a joint news conference during Trump's visit to Paris.
"We have asked our diplomats to work in that direction, so in the next few weeks a concrete initiative can be taken and managed by the P5," Macron said, referring to the five permanent members of the United Nations Security Council.