Rebel-held quarters of Syria's Aleppo came under heavy bombardment by regime forces on Saturday, as a senior security official said the real battle for control of the strategic northern city was yet to come.
A hold-out rebel district of Damascus was also pounded, a day after the United Nations deplored the failure of diplomacy to end a conflict that has reportedly claimed more than 21,000 lives in nearly 17 months.
Abdel Jabar Oqaida, commander of the Free Syrian Army in Aleppo, said the district of Salaheddin had "come under the heaviest bombardment since the battle began" on July 20 but that loyalists had "not managed to advance."
In what is also a war of words, a senior government security figure said "the battle for Aleppo has not yet begun, and what is happening now is just the appetizer."
"The main course will come later," he warned.
More than a week ago, a pro-government newspaper was already proclaiming what was to be the "mother of all battles" as heavy government reinforcements were being brought in.
And earlier this week, a security official said troops were "testing the terrorists' defence systems before annihilating them by carrying out a surgical operation."
The security official on Saturday said more reinforcements had arrived and that at least 20,000 troops were already on the ground.
"The other side are also sending reinforcements," the official added, referring to the rebels, who claim to have seized half the city since they poured in two weeks ago.
Because of restrictions on the free movement of journalists in Syria, none of the claims can be verified.
Echoing UN chief Ban Ki-moon's remarks on Thursday that 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 who heads the Syrian Observatory for Human Rights said 4,239 people, the vast majority civilians, died in July, bringing the overall toll since March 2011 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 city and rebels attempted early in the day to storm the state television building before being driven off by shelling, said the Britain-based Observatory.
State media said the army defended the site from "mercenary terrorist groups."
Meanwhile, the southern Damascus suburb of Tadamun was hit by some of the "most violent" shelling seen since loyalists launched a huge counter-offensive in the capital last month, the Observatory said.
The violence killed at least 60 people across Syria on Saturday, including at least eight in Aleppo province, the Observatory said. The dead comprised 35 civilians, 18 soldiers and seven rebels.
On Friday, a day after envoy Kofi Annan's resigned in frustration over the 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 it condemned 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.
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."
On Saturday, senior foreign ministry official Wang Kejian accused countries that oppose its position of pursuing their own geopolitical interests and "trying to hinder or even undermine the political settlement process."
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".
While progress on the political front "will be difficult," he said 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."
In other developments on Saturday, Qatar said Arab states will not accept a replacement for Annan unless the nominee's mandate is to clearly negotiate a transfer of power in Syria.
And 48 Iranian pilgrims were kidnapped from a bus in Damascus, Tehran's consul said, while an official in Ankara said another Syrian general had defected to Turkey.