France's outspoken Defence Minister Gerard Longuet slammed China and Russia on Monday for their veto of a UN resolution on Syria, and said such countries deserve a "kick in the ass".

"It is a disgrace for countries to refuse to assume their responsibilities," Longuet told Europe 1 radio. "Frankly, there are some political cultures that deserve a kick in the ass."

"Everyone must face up to their responsibilities. We must wake up those who accept conformity, and conformity that closes its eyes about a bloody dictator is unacceptable," he said.

Russia and China on Saturday blocked a UN Security Council resolution condemning Syria for its crackdown on protests, drawing condemnation from other global powers and the Syrian opposition.

French Foreign Minister Alain Juppe said on Sunday that Europe will strengthen sanctions imposed on Damascus in a bid to boost pressure on the regime and called the dual veto a "moral stain" on the United Nations.