BEIRUT: Ninety people died in Thursday's four bombings across Damascus, a violence monitoring group said, making it one of the bloodiest days in the Syrian capital since the outbreak of a revolt against President Bashar al-Assad nearly two years ago.

The Syrian Observatory for Human Rights, quoting figures it said were compiled from hospitals and other medical sources, said at least 60 of the dead were killed in a powerful car bomb blast in the Mazraa district of central Damascus, near the Russian Embassy and offices of Assad's ruling Baath Party.

The others were killed in three coordinated bombings in the north-eastern district of Barzeh, the Britain-based group said.

Syrian state media put the death toll from the Mazraa bombing at 53, with more than 200 wounded. Both activists and officials said most of those killed were civilians, including children.

In addition to the violence in the capital, more than 200 people were killed elsewhere including in the Damascus suburbs, the southern city of Deraa and northern commercial hub of Aleppo, bringing Thursday's death to around 300 - one of the highest in a single day, the Observatory said.

The United Nations says 70,000 people have died in Syria's conflict, the bloodiest and most protracted of the uprisings which have convulsed the Arab world in the last two years.

Russia, a staunch ally of Assad's, accused the United States on Friday of having double standards over the violence in Syria, saying Washington had blocked a U.N. Security Council statement condemning the Mazraa car bomb.

"We ... see in it a very dangerous tendency by our American colleagues to depart from the fundamental principle of unconditional condemnation of any terrorist act, a principle which secures the unity of the international community in the fight against terrorism," Foreign Minister Sergei Lavrov said.

There has been no claim of responsibility for the attacks, but the al Qaeda-linked hardline rebel group Jabhat al-Nusra has said it has carried out dozens of attacks in the past year, including devastating bombings in Damascus and Aleppo.