Syrian rebels have broken through to besieged areas in eastern Aleppo in an assault on a major government military complex meant to end a month-long siege, insurgents and a monitoring group say.
Pro-government media outlets denied the siege had been broken and a US State Department official said the situation on Saturday was "too fluid" to comment.
The heavy fighting and air strikes reported from the area seemed to indicate any passage that may have been opened would be far from secure enough for civilians to travel through.
Rebels have been trying to break through a thin strip of government-controlled territory to reconnect insurgent areas in western Syria with their encircled sector of eastern Aleppo, in effect breaking a government siege begun last month.
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The offensive against the government's Ramousah military complex, which contains a number of military colleges, began on Friday. Taking control of Ramousah and linking up with eastern Aleppo would isolate government-held western Aleppo by cutting the southern route out toward the capital Damascus.
It would also give rebels access to armaments stored in the base the Syrian army has used in the five-year conflict as a strategic platform from which to shell opposition targets.
Two rebel groups and a monitor said on Saturday they had broken the siege, but pro-government media outlets denied the claim and said the Syrian army was in fact regaining recently taken territory from rebels.
"We've seen reports but the situation is fluid and we aren't going to provide battlefield updates," the US State Department official told Reuters.
Jabhat Fatah al-Sham, formerly the al Qaeda-affiliated Nusra Front, said in an online statement: "Fighters from outside the city met their brother fighters from inside the city, and work is under way to establish control over remaining positions to break the siege."
A commander from more moderate rebel group also told Reuters the siege had been broken but said it was early days and matters were "not easy".
The UK-based Syrian Observatory for Human Rights, which monitors the war, said intense fighting and heavy air strikes meant no secure corridor had yet been established between the two rebel-held territories.
The Observatory, in its report on the Aleppo fighting, said rebels took control on Friday of the Weaponry College and part of the Artillery College. But the Syrian military news agency said later on Saturday the Syrian army had restored control over the Artillery College and had made the rebels withdraw from the Weaponry College.
Syrian President Bashar al-Assad wants to take full control of Aleppo, pre-war Syria's most populous city, which has been divided between rebel and government-held areas. Such a victory would be a crushing blow to the insurgents.
A quarter of a million civilians are thought to still live in Aleppo's opposition-controlled eastern neighbourhoods, effectively under siege since the army and allied militia cut off the last road into rebel districts in early July.
