The Syrian government has said women and children can leave besieged areas of the city of Homs in the centre of the country.
The announcement came after negotiators from the warring sides discussed humanitarian gestures on a second day of face-to-face talks in the Swiss city of Geneva.
Homs, occupying a strategic location, has been a key battleground. President Bashar al-Assad's forces retook many of the surrounding areas last year, leaving rebels under siege in the city centre, along with thousands of civilians.
In-depth coverage of escalating violence across Syria
Hundreds of families in the Old City have lived under the siege for nearly 18 months now, with frequent shelling and very limited supplies.
Lakhdar Brahimi, the UN-Arab League envoy, said on Sunday he understood that the women and children would be free to leave Homs immediately.
The Syrian authorities also agreed to allow humanitarian aid convoys in - as soon as Monday.
Faisal Maqdad, the Syrian deputy foreign minister, said after Sunday's meetings that the government would let women and children leave the city centre if rebels gave them safe passage.
"If the armed terrorists in Homs allow women and children to leave the Old City of Homs, we will allow them every access," he said.
"Not only that, we will provide them with shelter, medicines and all that is needed. We are ready to allow any humanitarian aid to enter into the city through the ...arrangements made with the UN."
In Homs, however, opposition activists said rebels demanded a complete end to the blockade and opposed a limited ceasefire.
Brahimi, who presided on Saturday over the first direct meeting between the two delegations, met both together again on Sunday morning, before holding discussions with each side separately in the afternoon.
He said opposition delegates, who have asked for the release of nearly 50,000 detainees, had agreed to a government request to try to provide a list of those held by armed rebel groups - though many of these groups, fighting among themselves, do not recognise the negotiators' authority.
Maqdad said the Syrian government had examined an opposition list of 47,000 people believed to have been arrested by Assad's forces and found most had either never been held or were now free.
He also denied that any children were being held.
Brahimi hopes to begin discussion of a UN plan for a transitional government at another joint session on Monday, .
There was little sign of a softening of positions on the core issue - whether or not Assad should quit now, as the opposition and their Western and Arab backers say was agreed by a UN conference at Geneva 18 months ago.
An adviser to Assad, Bouthaina Shaaban, demanded that the UN text calling for a political transition should be amended.
The government was ready to discuss the Geneva Communique, she said.
However, she said, "Geneva is not the Quran. It's not the Gospel ... Geneva was issued in June 2012. We are now January 26, 2014. The ground has changed. We change according to what this reality requires".
Speaking for the opposition National Coalition, Louay Safi said Monday's session with Brahimi would show if the government was willing to negotiate: "Tomorrow we start talking about transition from dictatorship to democracy. The regime is ... stalling."
However, Maqdad repeated the government position that Assad can stay and win an election, saying: "The president of the Syrian Arab Republic stays until the Syrian people says something else."
And Omran Zoabi, the Syrian information minister, said there was no chance of Assad surrendering power.
"If anybody thinks or believes that there is a possibility for what is called the stepping down of President Bashar al-Assad, they live in a mythical world and let them stay in Alice in Wonderland," he said.
Meanwhile, on the ground, Syrian rebels and government troops clashed in some districts of Damascus, a Britain-based monitoring group said.
"Fierce fighting raged between rebels and troops in Jobar [in eastern Damascus] and the Port Said area of Qadam [in the south]," the Syrian Observatory for Human Rights said.
A rebel mortar round hit the city's central Qassaa district, wounding seven people, state news agency SANA reported.
Elsewhere, troops shelled opposition-held Douma, northeast of the capital, the Syrian Observatory said.
|Scepticism over news allowing women and children to leave Homs
It also reported that the siege of the Yarmouk Palestinian camp in southern Damascus by regime troops claimed six more lives on Sunday because of food and medical shortages.
In the northeast, 26 fighters were killed in battles between fighters from the al-Qaeda-affiliated Jabhat al-Nusra and the Islamic State of Iraq and the Levant (ISIL), and Kurds near Ras al-Ain, a majority Kurdish town, according to the Syrian Observatory.
Kurds have fought fierce battles against armed opposition groups.
ISIL sees the ethnic Kurds as "heretics" and an obstacle to setting up an Islamic "caliphate" stretching from Iraq to Syria.
Aleppo, once Syria's commercial capital and now destroyed by nearly 18 months of all-out war, also witnessed fresh violence on Sunday.