BEIRUT -- Syria’s government secured a deal to restore its authority over another rebellious Damascus suburb on Thursday while Syrian rebels captured new ground in a lightning advance on the central city of Hama and suspected government airstrikes killed 25 civilians in the surrounding province.

The Syrian capital’s western suburb of Moadamiyeh, which a U.N. report said was gassed with toxic sarin in 2013, has suffered a three-year government siege that left its estimated 28,000 residents with dwindling food and medical supplies.

On Thursday, Moadamiyeh’s residents agreed to let President Bashar Assad’s government restore its security presence and political institutions in the suburb, according to Hassan Ghadour, a resident and leading negotiator of the deal.

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Ghadour said 200 gunmen who did not wish to give up their arms would be allowed safe passage to rebel-held areas in Syria’s northwestern Idlib and Aleppo provinces. The implementation to the agreement is expected to begin Friday.

A local activist in the suburb, Dani Qappani, said the residents had no desire to negotiate with Assad’s government but that their “circumstances grew too difficult.”

The development came as an uneasy truce continued to hold on Thursday between Turkish troops and Kurdish-led forces in northern Syria, despite Ankara’s vow that it would never negotiate with what it calls a “terror organization.” The United States has called on both sides to stop fighting each other following Turkey’s incursion into the area last week, and instead focus on defeating the Islamic State of Iraq and Syria (ISIS).

Elsewhere in Syria on Thursday, at least 25 civilians, including six children, were killed in suspected government airstrikes on Hama province as rebels made new gains there, activists said.

The Hama-based Syrian Press Center, an activist group operated by Ahmed al-Ahmed, said at least 10 people were killed when warplanes struck a crowd of people displaced from Suran, a town north of the city of Hama, which was seized by opposition fighters. Another 15 people were killed further to the west, the center said.

The rebel offensive is led by an ultraconservative Islamic group, Jund al-Aqsa, and several factions from the Western-backed Free Syrian Army. In the past three days, the insurgents have pushed their way from the north of the province, where they are usually based, south toward government-held areas.

Al-Ahmed said the rebels were only 5 miles away from the provincial capital, Hama. They have taken over a government military base and control several towns along the highway linking Hama to Damascus, following a “surprising” government retreat, he said.

The advances in Hama are significant because if rebels control the city and the highway they can sever government supply lines and deprive Assad of a traditional stronghold. Fighting is now concentrated around a hill outside the city of Hama, al-Ahmed added.

Al-Ahmed, who spoke from Turkey, said government forces in Hama province may have been weakened because many troops were transferred to the city of Aleppo, where they have gotten bogged down in vicious fighting with advancing rebels.

The Britain-based Syrian Observatory for Human Rights confirmed the insurgents’ advance and said a series of airstrikes since early Thursday killed at least 25 civilians, including six children, in northern Hama province.

Syria’s state news agency, SANA, said government warplanes killed 10 “terrorists” in northern Hama.

At a press conference in Geneva, the U.N. envoy to Syria warned of Syrian government’s use of siege tactics to force evacuations of residents from specific areas, citing the example of Daraya, a neighboring suburb of Moadamiyeh from where residents were evacuated after it was surrendered to the government.

“After Daraya, we may have other Darayas,” Staffan de Mistura said.

Government forces kept Daraya under tight siege for four years after the suburb evicted security forces in 2012, and ultimately secured an agreement for the estimated 6,000 remaining civilians to leave the area last week. De Mistura acknowledged such examples, if repeated, “could be a strategy” that is taking place.

De Mistura’s humanitarian adviser, Jan Egeland, says the U.N. humanitarian task force for Syria had “failed the people of Daraya.” He warned that sieges on al-Waer in Homs and Madaya, near Damascus, could force similar exoduses.

The U.N. envoy also said he was preparing “a quite clear political initiative” to help revive the stalled Syria peace talks aimed at resolving the country’s devastating civil war, now in its sixth year. De Mistura said the “important” initiative will come ahead of a planned Sept. 21 meeting on Syria during the U.N. General Assembly ministerial meeting in New York.

New Zealand’s U.N. Ambassador Gerard van Bohemen, whose country holds the Security Council presidency, said members are expected to discuss the “political initiative” that de Mistura is preparing to help revive the stalled talks at the high-level council meeting on Sept. 21.

Van Bohemen told reporters at U.N. headquarters in New York on Thursday that the council session will be chaired by New Zealand Prime Minister John Key, who has invited leaders of the 14 other council nations to attend.

He said New Zealand wants “to shine a spotlight” on “the greatest crisis of our time.”

De Mistura, the U.N. envoy, had hoped to resume talks between Assad’s government and the main opposition group in August, having set two target dates during the month. He suspended the talks in April amid renewed fighting.