Syria's state television quoted the Health Ministry as saying 25 people were killed and 175 people injured in Aleppo in two explosions -- apparently car-bombings -- The New York Times reported.
State media said the blasts near a military intelligence directorate and police headquarters were the work of "terrorists." Images showed shattered windows, crumpled vehicles and a mix of concrete blocks and other materials on the ground.
In Turkey, Capt. Ammar al-Wawi, a spokesman for the Free Syria Army, an opposition group of military defectors, denied involvement in the Aleppo explosions, blaming the government for carrying out the attacks.
"This regime is playing a well-known game, seeking to distract the world's attention from the massacres in Homs," Wawi said.
Activists said the incessant bombardment of many parts of Homs by security forces since Saturday had killed more than 400 people and left the city isolated, the BBC reported. Necessitates such as food and medical supplies are dwindling and people have said they fear leaving their homes because of snipers.
CNN showed video taken with cellphones of residents sneaking out at night to bury their dead because the risk of being fired upon by government forces during the day is too great.
Activist organizations estimated Thursday's death toll in Homs could be from 50 to more than 100, the Times said. The Syrian Observatory for Human Rights, based in Britain, estimated the death toll in Homs was about 50 but said communication with the city was hampered by intermittent cellphone service.
The figures could not be independently confirmed because of restrictions President Bashar Assad's government placed on foreign journalists.
"The children will die here," Basil Abu Fouad, a resident of Homs' reputed opposition stronghold district of Baba Amr, told the British newspaper The Guardian by phone from a basement.
"All the people want is to escape. They can smash this place if they want," he said. "We just want to get out of there. But they won't allow us."
U.S. President Barack Obama has condemned the "outrageous bloodshed."
The opposition called for nationwide protests Friday to denounce Russia's veto of a U.N. Security Council resolution that, among other things, calls on Assad's government to stop killing its own people. China also vetoed the resolution.
Russia's Deputy Foreign Minister Sergei Ryabkov said the opposition "bore full responsibility" because it wouldn't enter talks with the government and charged Western leaders of being an "accomplice," the BBC said.
Members of the Syrian National Council, an umbrella of opposition groups based in Istanbul, Turkey, met in Qatar Thursday ahead of a weekend Arab League summit on Syria.
Participants told Gulf News the league, at its Cairo meeting, could recognize the council as the Syrian people's legitimate representative.
The council and 22-member league, along with the United States, Turkey and other European nations, have all called for Assad's exit and are pressing to form a group to tighten sanctions on the Assad regime and get humanitarian aid to attacked Syrians.
The nine-member Gulf Cooperation Council is to meet Sunday to address the Syrian crisis.
Another opposition group, the Syrian National Coordination Body for Democratic Change, met with leaders in Beijing.
The group said Thursday the meeting was meant "to convey to Chinese officials the true picture of the need to develop a political program that paves the way to the transitional stage, so as to avert the dangers of a spiral of violence, civil war and foreign military intervention."
Foreign Ministry spokesman Liu Weimin explained China's position to the group and called on all sides to immediately stop the violence, China Daily reported.
"The Syrian government should earnestly fulfill its promises to start an inclusive reform process that has wide participation, and resolve disputes via talks and consultations," Liu said, adding China was a friend of the Syrian people, the newspaper reported.
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