BEIRUT, Lebanon — Syrian activists said Monday that the southwestern city of Dara’a was under siege in what seemed to be part of an extended campaign by the Syrian government to regain control of the area, the birthplace of the uprising against President Bashar al-Assad.

After shells hit a field hospital on Sunday, killing doctors and nurses, medical services and supplies were in short supply, said Kayssar Habib, a spokesman for the opposition Sham News Network in Dara’a. He and other activists also said that summary executions were now on the rise in the city.

“The regime forces are taking men out of shelters and executing them,” Mr. Habib said. “Most of them are civilians.”

House-to-house raids directed at supporters of the opposition seem to be expanding elsewhere as well. On Monday, activists circulated a video online showing the unidentified bodies of 10 people who activists said were civilians killed in the Damascus neighborhood of Al Qaboun. In the video, the bodies, including several women, appeared on a street corner, with many seemingly bearing the marks of torture.