Fighting shook Syria on Saturday, with rebels trying to seize the state television building in Aleppo and Damascus bombarded, as the UN deplored the failure of diplomacy to end the conflict.
Echoing UN chief Ban Ki-moon's remarks a day earlier that the violence was intensifying, a watchdog said July was the deadliest month since the uprising against President Bashar al-Assad's regime erupted in March 2011.
Rami Abdel Rahman of the Syrian Observatory for Human Rights said 4,239 people, the vast majority civilians, died in July, bringing the overall toll in nearly 17 months of fighting to more than 21,000.
"The death toll is escalating," Abdel Rahman said, noting June had been the second-deadliest month.
And with thousands more displaced, lacking basic needs and unable to get medical treatment, the Red Cross and this month's UN Security Council president, France, highlighted humanitarian concerns.
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 Britain-based Observatory.
"Rebel forces planted explosives (at the TV station), and regime forces shelled the area" before the rebels withdrew, it said.
State media said the army defended the site from "mercenary terrorist groups."
There was also fierce fighting in the rebel-held quarters of Salaheddin and Seif al-Dawla, the Observatory said, as troops fought to retake the city two weeks after rebels moved in and claimed to have captured half of it.
Meanwhile, the southern Damascus suburb of Tadamun was hit by some of the "most violent" shelling seen since troops launched a huge offensive against rebels in the capital last month, the Observatory said.
The violence, which killed at least 13 people across the country on Saturday, has been relentless. Another 84 died around the country -- 46 civilians, 19 rebels and 19 soldiers -- a day earlier, the Observatory said.
On Friday, following envoy Kofi Annan's resignation in frustration over failure of an April peace plan to take hold, UN chief Ban warned world powers they must overcome their rivalries to put an end to a "proxy war" in Syria.
And the UN General Assembly voted overwhelmingly to condemn the Security Council for its failure to act and criticise the regime for using heavy weapons.
Ban said growing radicalisation and extremism had been predicted at the start of the uprising, as had been a "proxy war, with regional and international players arming one side or the other.
"All of these dire predictions have come to pass," he told the General Assembly.
The Security Council had become paralysed by divisions, he said, adding: "Now, with the situation having worsened, they must again find common ground."
Following the General Assembly vote, US ambassador Susan Rice said that, "despite the continued opposition of an increasingly isolated minority, the overwhelming majority of UN members clearly stands resolutely with the Syrian people."
That was an allusion to Russia and China, who voted against the resolution and who had already vetoed three Security Council resolutions on Syria.
But Russian Ambassador Vitaly Churkin said the assembly 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 Damascus would "cause further escalation of the turmoil and let the crisis spill over to other countries in the region."
Syria strongly opposed the resolution and its UN envoy, Bashar Jafaari, accused Saudi Arabia, Qatar and other Gulf states of arming rebels.
South Africa, while voting in favour, said the text should have been tougher on the opposition.
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 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.
France's UN ambassador Gerard Araud said Paris would use its presidency of the Security Council to push for humanitarian aid for Syrians, warning Russian and Chinese intransigence could lead to "a final disaster".
"Progress on the political front will be difficult, I have to confess," said Araud.
But things can be done "on the humanitarian front, because above and beyond the deadlock on the Security Council or the resignation of Annan, there is the suffering of the Syrians."
The International Committee of the Red Cross called on all parties to respect international humanitarian law.
Robert Mardini, ICRC operations chief for the Middle East, reminded both sides that civilians must never be targeted and that medical services be protected.