President Bashar al-Assad has been under international pressure to end a crackdown that began in March 2011 with an attempt to crush an anti-government protest movement that has grown into an armed rebellion.
Al-Assad has denied opposition assertions that he is targeting civilians, and he has repeatedly described the crackdown as a fight against "armed terrorists" bent on destabilizing Syria.
France plans to propose that the United Nations be given the power to enforce Annan's peace plan, including considering the possibility of implementing a no-fly zone, to end the bloodshed.
"If you can't call it a civil war, then there are no words to describe it," said French Foreign Minister Laurent Fabius, who became the first Western government official to label it as such.
He called on Russia to reverse its opposition to international action led by the United Nations. Russia and China, trade allies of Syria, have blocked Security Council attempts to pass a resolution calling for an end to the violence and for al-Assad to step down.
Fabius is urging Russia to authorize the use of force in Syria under Chapter 7 of the Charter of the United Nations, which allows for action to stop the escalation of targeted violence.
"The time to make a decision has arrived," Fabius said.
Russia has repeatedly refused to support any action against Syria, accusing the West of using a Security Council resolution that called for the protection of civilians in Libya to support its successful effort last year to oust Moammar Gadhafi from power.
Meanwhile, a human rights group accused al-Assad's forces of killing civilians in organized attacks.
In a 70-page report, Amnesty International listed crimes against humanity and war crimes by Syrian forces as part of a government attempt to take revenge on towns and communities suspected of supporting rebels.
The rights group called on the U.N. Security Council to refer Syria to the International Criminal Court in the Hague to face charges.
U.N. advisers on the prevention of genocide issued a statement Thursday saying that the recent mass killings of civilians in Houla and Qubeir represent "an alarming escalation in targeted attacks against civilians," and urged that the Security Council consider the request of the High Commissioner for Human Rights to refer the situation to the International Criminal Court at the Hague.
"With the increasing violence and deepening sectarian tensions, the risk of further mass atrocity crimes is high," their statement said. "The time for action is now."
Opposition groups estimate more than 12,000 people have died in the uprising.