But Louay Hussein, the leader of a nascent opposition party, said the Arab League should have pressed ahead with an initial group of about 40 monitors once Syria said on Nov. 2 that it accepted the peace plan.

The sanctions include a travel ban against scores of senior Syrian officials, a freeze on government assets in Arab countries, a ban on transactions with Syria’s central bank and an end to all commercial exchanges with the Syrian government.

Mr. Moallem sidestepped a question about why the Assad government had not presented the results of a promised investigation into the jailing and torture of children in the southern town of Dara’a, the event that ignited the uprising nationwide.

In Geneva, however, an independent commission organized by the United Nations Human Rights Council released a long-awaited report on rights abuses by Syria’s security forces. Based on interviews with 223 victims and witnesses, the report documented what it described as “patterns of summary execution, arbitrary arrest, enforced disappearance, torture, including sexual violence, as well as violations of children’s rights.”

The commission expressed concerns that “crimes against humanity have been committed.”

Mr. Moallem said Syria rejected any assertions that its military was responsible for civilian bloodshed, saying both the West and the Arab world refused to accept the Assad government’s view, which is that the country has been the target of armed gangs financed from abroad.

He presented a gruesome, 10-minute video that showed what he said were photos of murdered security personnel, some of them hacked to death. As in most such video recordings presented by both sides, the contents were impossible to confirm independently.

Syria rarely grants visas to Western reporters, and a sudden invitation into the country seemed intended both to highlight the news conference and to address demands from the Arab League that more international correspondents be given entry. Such visits are heavily supervised, however, starting at the border.