The United States said Monday nearly 128,000 people face arbitrary detention by the Syrian regime and called for their release.
"This practice is unacceptable," US Ambassador Kelly Craft told the UN Security Council at its monthly meeting on the conflict in Syria.
"The Assad regime must release detainees and provide international monitors access to detention centers," she said.
Syria's President Bashar al-Assad has declared several amnesties of prisoners since the conflict began in 2011 -- notably in 2014, 2018, and in mid-September.
Russian Deputy Foreign Minister Sergey Vershinin called for the "elimination of terrorists in Idlib" province, while stressing that utmost care be taken to spare civilians.
The conflict has claimed the lives of an estimated 370,000 people.
"The time has come to encourage and not impede Syria's return to the Arab family," Vershinin said.
Syria was suspended from the Arab League in 2011, and the issue of its return has divided the organization's members for more than a year.
Security Council members welcomed the creation of a UN-sponsored constitutional committee by the government and the opposition, after two years of arduous negotiations.
The UN envoy for Syria, Geir Pedersen, said the committee's formation marked the first concrete political agreement between the government and the opposition.
"It is also a shared promise to the Syrian people to try to agree under the auspices of the United Nations on new constitutional arrangements for Syria -- a new social contract to help repair a broken country," he said.
The committee's 150 members are supposed to hold their first meeting October 30 in Geneva.
Its revision of the constitution is viewed by the UN as a first step toward holding elections that would include the Syrian diaspora.
Last week, the Syrian regime stressed that no deadline has been set for the committee to conclude its work.