BEIRUT — Syrian activists said Monday that pro-government gunmen killed at least 16 people, including some children, in a rebel stronghold recaptured by the government, fueling concerns the government is carrying out reprisals in territory it has taken back.

State media in Damascus, which often ignore activists’ claims, confirmed killings in Homs but blamed “armed terrorists,” as they frequently call those behind the yearlong uprising against President Bashar Assad’s regime.

At the United Nations, the U.S. and Russia clashed after Secretary-General Ban Ki-moon appealed to the divided Security Council to speak with one voice and help Syria “pull back from the brink of a deeper catastrophe.” Washington and Moscow both called for an end to the bloody conflict — but on different terms, leaving prospects for U.N. action in doubt.

The reports of killings in the battered city of Homs added to concerns that the hundreds of civilian deaths in the fighting would be compounded by reprisals against opposition supporters in recaptured towns.

Fresh from stamping out rebel centers of resistance in Homs, government forces are pressing on with new offensives in central and northern Syria.

The main opposition group, the Syrian National Council, called for “immediate” Arab and international military intervention, including setting up safe corridors for humanitarian aid and a no-fly zone to protect civilians.

The Britain-based Syrian Observatory for Human Rights said at least 16 people were killed Sunday in Homs, while the Local Coordination Committees said 45 were killed.

Both said children were among the dead.