New allegations about Syria's brutal crackdown on anti-government protesters are sparking U.N. calls for the regime to be tried for crimes against humanity.

The United Nations' top human rights official Friday called for Syria to be referred to the International Criminal Court. Navi Pillay told a meeting of the U.N. Human Rights Council in Geneva the Syrian government's ruthless behavior has even resulted in the deaths of hundreds of children.

She also called on the international community to “take urgent and effective measures” to protect the Syrian people.

A U.N. appointed investigator told the council Friday that 307 children have been killed by state forces since the protests began eight months ago. Paulo Pinheiro also said 56 children were killed in November, making it the deadliest month for Syrian children so far.

Syria condemned investigator's report, telling the Associated Press the report was not objective.

The latest allegations come one day after the U.N. human rights commissioner said the Syrian crackdown on anti-government protesters had degenerated into a civil war, and that the total number of Syrians killed in the unrest now exceeds 4,000.

U.S. State Department spokesman Mark Toner said Thursday the violence in Syria should not be characterized as a civil war, because, he said, the government is overwhelmingly responsible for the use of force.

Syria has refused to end the crackdown, saying it is a necessary response to attacks by “armed terrorists” on civilians and security personnel.

Meanwhile, a report Thursday by the Russian news agency Interfax says Moscow delivered supersonic cruise missiles to Syria, despite calls from the U.S. and Europe for a weapons embargo against the government.

The European Union said it is tightening sanctions on Syria. EU officials also said they added 11 more entities and 12 more individuals to a blacklist hit by travel bans and asset freezes.