President François Hollande of France told the United Nations General Assembly on Monday that his country would “shoulder its responsibilities” in global efforts to end the fighting in Syria, but that the conflict could be resolved only if President Bashar al-Assad was removed from power.

France mounted its first airstrikes against the Islamic State militants in Syria over the weekend.

Mr. Hollande told the Assembly that to blame only the Islamic State for the massacres of civilians in Syria would be to pardon “the regime that created this organization.” The millions of refugees from Syria who have flooded into neighboring countries and into Europe are not only “fleeing a war, but fleeing the regime of Bashar al-Assad,” he said.

“Assad is the origin of this problem, and cannot be part of the solution,” Mr. Hollande said.

His comments seemed directed at Russia, which has recently stepped up its support for Mr. Assad and has proposed resolving the conflict through talks between his government and opposition groups while an international coalition battles the Islamic State. In a speech earlier on Monday, President Vladimir V. Putin of Russia warned that ousting Mr. Assad would be a mistake.

Without mentioning Russia by name, Mr. Hollande also criticized its efforts to shield the Syrian government from action by the Security Council. “In cases of mass atrocities,” he said, “the veto should not be used.” Only the council’s five permanent members — Britain, China, France, Russia and the United States — wield vetoes.