The Local Coordination Committees, an opposition group, said that more than two dozen people had also been killed in the city of Hama, but did not elaborate on the circumstances of the deaths. Reuters, citing activists in Hama, said that government security forces had lined up and fatally shot 13 men and boys from one extended family in the village of Kfartoun in Hama Province. Neither the death tolls, nor the report of the massacre, could be independently confirmed.

Activist groups reported dozens of people killed in heavy fighting in Idlib Province as well.

Secretary of State Hillary Rodham Clinton and several foreign ministers of European and Arab countries met in London on Thursday ahead of the international “Friends of Syria” meeting in Tunis. They discussed urgent efforts to provide humanitarian assistance, especially medical supplies to Homs and other battered cities. A senior State Department official traveling with Mrs. Clinton said that countries were ready to provide considerable assistance “within days” through United Nations relief agencies, but that “the real challenge is the access issue.”

In a press conference Thursday, Mrs. Clinton moved the United States a step closer to recognizing the Syrian National Council, an exile opposition group, though a formal recognition is not expected in Tunis. She also said later, discussing growing pressure on Mr. Assad: “There will be increasingly capable opposition forces. They will — from somewhere, somehow — find the means to defend themselves as well as begin offensive measures. And the pressure will build on countries like Russia and China because world opinion is not going to stand idly by.”

Both countries recently vetoed a United Nations Security Council resolution supporting a plan to end the bloodshed. Russia has said it will not attend the Tunisia meeting and news reports on Thursday said China had not committed, blunting the gathering’s chances of securing strong action against Mr. Assad’s government.