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Troops with air cover fought rebels for control of a television centre in Syria's commercial capital Aleppo as clashes also raged in Damascus on Saturday, a watchdog reported.
Loud explosions shook Aleppo as fighter jets and helicopter gunships overflew the northern city and rebels attempted to storm the state TV building, said the Syrian Observatory for Human Rights.
"Rebel forces planted explosives (at the TV station), and regime forces shelled the area" before the rebels withdrew, said the Observatory.
State media said the army defended the site from "mercenary terrorist groups."
In Damascus, the Observatory reported that the southern suburb of Tadamun was hit by some of the "most violent" shelling that it has seen since government forces launched a huge offensive against rebels in the capital last month.
The violence, which killed at least 13 people across the country on Saturday, has been relentless, with the international community struggling to find common ground on ending the nearly 17-month conflict.
On Friday, 84 peopled died around the country -- 46 civilians, 19 rebels and 19 soldiers, the Observatory said.
UN chief Ban Ki-moon warned world powers that they must overcome their rivalries to put an end to what he described as a "proxy war" in Syria.
The secretary general spoke ahead of a UN General Assembly vote that overwhelmingly condemned the Security Council for its failure to act and the regime of President Bashar al-Assad for using "heavy weapons".
Ban evoked the UN's failure in the 1995 Srebrenica massacre in Bosnia and warned the divided council that "the immediate interests of the Syrian people must be paramount over any larger rivalries of influence".
The UN leader said growing radicalisation and extremism had been predicted at the start of the conflict in March 2011.
"The next step was also forewarned: a proxy war, with regional and international players arming one side or the other. All of these dire predictions have come to pass," Ban told the General Assembly.
The Security Council had become paralysed by divisions over Syria, he said, adding: "Now, with the situation having worsened, they must again find common ground."
After his address, the General Assembly overwhelmingly passed a Saudi-drafted resolution criticising the Security Council's failure to act and condemning Assad's use of heavy weapons.
The resolution said members deplored "the Security Council failure to agree on measures" to make Damascus carry out UN demands to end the bloodshed.
Condeming the regime's use of "heavy weapons including indiscriminate shelling from tanks and helicopters," it passed by a vote of 133-12, with 31 abstentions.
"Despite the continued opposition of an increasingly isolated minority, the overwhelming majority of UN members clearly stands resolutely with the Syrian people," US Ambassador Susan Rice said after the vote.
But Russian Ambassador Vitaly Churkin warned it gave "blatant" support to Syrian rebels and that its backers were the countries providing "mercenaries and arms" to the opposition.
China's deputy ambassador, Wang Min, said pressuring only the Syrian government will "cause further escalation of the turmoil and let the crisis spill over to other countries in the region."
Russia and China have so far vetoed three Security Council resolutions on Syria.
Syria strongly opposed the resolution and its UN envoy, Bashar Jafaari, accused Saudi Arabia, Qatar and other Gulf states of arming rebel groups.
The ambassador said he and his family had been the target of death threats.
"There have been several threats of murder against me and various Syrian diplomats from sites that exist in Saudi Arabia and Qatar and the United States," he told the General Assembly.
South Africa, while voting in favour, said the resolution should have been tougher on the opposition.
The head of the opposition Syrian National Council said the resolution showed Assad's regime had lost legitimacy.
"This vote confirms that... the international community does not believe in its legitimacy anymore," said SNC director Abdel Basset Sayda, adding that the rebels would not pull out of Aleppo.
"The Free (Syrian) Army did not withdraw, and will not withdraw from Aleppo, and we are in contact with them to provide them with supplies," Sayda said.
A Syrian security official said troops were "testing the terrorists' defence systems (in Aleppo) before annihilating them by carrying out a surgical operation."
Russia expressed serious concern over rebel attempts to gain control of Aleppo and condemned foreign nations for providing the opposition with military supplies.
"Moscow is very worried by the dangerous development in the situation, the violence and provocations aimed at expanding the scope and the cruelty in the civil war," said the foreign ministry in Moscow.