Syrian President Bashar al-Assad said on Wednesday that the army was fighting for the nation's future as UN officials said the regime was using fighter jets against rebels armed with tanks.
Buoyed by capturing three Aleppo police stations on Tuesday, the rebels said they were now turning their sights on the regime's intelligence apparatus in the battle for Syria's commercial capital, which has raged since July 20.
Assad said the campaign to crush the uprising, which is now in its 17th month, was vital to Syria's future. Washington said his call to continue the "slaughter" which human rights monitors say has already killed more than 20,000 people was "despicable".
"The army is engaged in a crucial and heroic battle... on which the destiny of the nation and its people rests," he said, in a speech carried by the official SANA news agency.
"The enemy is among us today, using agents to destabilise the country, the security of its citizens... and continues to exhaust our economic and scientific resources."
Washington mocked the Syrian leader as "cowardly" for not delivering his speech to mark armed forces day in public.
"We think it's cowardly quite frankly to have a man who's hiding out of sight be exhorting his armed forces to continue to slaughter the civilians of his own country," said a US State Department spokesman, Patrick Ventrell.
"We think it's despicable to be exhorting his armed forces to continue this slaughter, and this bloodshed."
Syrian Defence Minister General Fahd Freij vowed that the "terrorists" would soon be defeated.
"Seeing your heroic actions, I can assure the Syrian people that victory over this huge conspiracy is near," Freij said.
But his optimism was belied by the fierce fighting in Aleppo, where rebel fighters continued to put up determined resistance to an army counter-offensive launched on Saturday.
The United Nations said its military observers in Syria had seen the military use a fighter jet to strike the rebels in Aleppo, who were now armed with tanks.
"The observers now have confirmed information that the opposition is in possession of heavy weapons including tanks in Aleppo," UN spokesman Martin Nesirky told reporters at the UN headquarters.
The UN observer mission also reported seeing a fighter jet attacking the city in a field visit to the city on Tuesday.
AFP correspondents on the ground have reported that rebels have captured a number of tanks, and some armoured units have defected with their vehicles.
Nesirky stressed that UN leader Ban Ki-moon wants united international pressure on both sides in the civil war.
He said pressure should be brought to bear on "not just the Syrian government forces -- who of course bear the lion's share of the responsibility for what is happening -- but also on the opposition forces, to ensure that they do heed the calls, that they do stop the fighting."
The FSA's military chief in Aleppo, Colonel Abdel Jabbar al-Oqaidi, said the rebels had "thousands" of fighters in the city.
"The regime says it is fighting 'terrorist groups.' We tell the regime that we will chase them because they are the terrorists," Oqaidi told AFP.
"We will go after them in the whole of Aleppo, until the city is liberated."
Rebel commander Ferzat Abdel Nasser, an army general who defected a month ago said: "The most important thing is to take over the intelligence branches. If these sites fall, victory is possible."
-- Food needs growing --
FSA spokesman Kassem Saadeddine said the rebels controlled half of Aleppo city and most of its province.
"We hope to create a safe zone in Aleppo and (the northwestern province of) Idlib," on the border with Turkey, said FSA spokesman Kassem Saadeddine. Idlib and Aleppo are northern Syria's two main cities.
A safe zone would enable rebels to bring in weapons more easily from nearby Turkey, and to set up a more organised military structure.
The World Food Programme said it had sent food assistance for distribution to 28,000 people in Aleppo over the next few days.
"The humanitarian situation is deteriorating in Aleppo and food needs are growing rapidly," the UN agency said.
The United Nations says that some 200,000 of the city's estimated 2.7 million population have fled their homes, many of them taking refuge in schools and other public buildings.
Nationwide, at least 135 people were killed in violence on Wednesday -- 74 civilians, 43 soldiers and 18 rebels, the Britain-based Syrian Observatory for Human Rights said.
On Tuesday, 124 people were killed nationwide, around half of them in Aleppo, it said.
The Free Syrian Army hit out at the announcement by a civilian dissident group in Cairo on Tuesday that it intended to set up a government in exile.
"This government in exile was stillborn because it was made by a single group that does not represent the whole of the opposition," the FSA spokesman told AFP.
Veteran human rights activist Haytham al-Maleh, 81, had told reporters that he had been tasked with forming a government-in exile, adding that he would consult "with the opposition inside and outside."