Syrian rebels say a coalition of armed anti-government groups, the Army of Conquest, has captured all of a strategically important military base in the northern city of Aleppo.
However, Syrian state television disputes the claim, saying that government forces pushed the rebel fighters back, killing hundreds of them in the process.
The opposition forces, who already control the countryside and areas southwest and east of Aleppo, insist they are still control of the base in the Ramosa quarter in southwestern Aleppo.
Saturday's conflicting claims came a day after the Army of Conquest said they had stormed the major army artillery base.
READ MORE: Life among barrel bombs for Aleppo's children
"The rebels have seized parts of these schools, but the army has begun a counteroffensive backed by air cover to chase them out," Rami Abdel Rahman, head of the UK-based monitoring group Syrian Observatory for Human Rights (SOHR), told AFP news agency on Friday.
"If the rebels can take control of these schools, they will cut the supply route into regime-held districts of western Aleppo and they must seize the adjoining area of Ramosa to lift the siege on the rebel districts."
The artillery base is almost 2km from the besieged opposition area.
It has a huge supply of ammunition and is used regularly to shell parts of the city held by opposition forces.
"There are two suicide bombers who have driven into regime posts inside the artillery base," Abu al-Walid, a fighter with Ahrar al-Sham, told Reuters news agency on Friday, adding that there was fighting inside the base.
Hundreds of fighters clashed with government troops only a few hundred metres from each other in parts of the artillery base after breaking into government defences around the heavily fortified compound, the rebels said.
For its part, the Syrian army said the attack on the artillery base and two major military academies had been foiled, with hundreds of fighters killed and much of their armoured vehicles and tanks destroyed.
It said the assault was the biggest by rebels against government-held areas in the last few years.
"Today there was a large-scale attack by the terrorist armed groups and they used all types of weapons but we are fighting this attack and will defeat them," Brigadier-General Deeb Bazi, the head of one of the military academies targeted, told Reuters.
OPINION: Syria's civil war is a post-factual conflict
Al Jazeera's Reza Sayah, reporting from Gaziantep, on the Turkish side of the Syria-Turkey border, said the fighting in Aleppo is desribed by many as "the decisive battle for Syria".
"The impression is that if the government manages to take over Aleppo, they will gain momentum and take away leverage from the rebels - there will no longer be an incentive to go on the negotiating table with the rebels," he said.
"But the impression also is that if the rebels control Aleppo, they will still have leverage and a bargaining chip to get the Syrian government to the negotiating table."
'Decisive battle for Syria'
Once Syria's economic powerhouse and the country's biggest city, Aleppo has been divided between government forces and rebels since the summer of 2012.
The government siege of opposition-held districts began on July 17 and has raised fears of a humanitarian crisis for some 300,000 people trapped in rebel-controlled areas.
According to the SOHR, at least 115 civilians, including 35 children, have been killed in the city since the fighters began an assault on Sunday to break through a strip of government-controlled territory in order to reconnect their area of control in western Syria with the encircled sector of eastern Aleppo.
The deaths include 65 people, among them 22 children, killed in opposition fire on government neighbourhoods, according to the SOHR, which gathers information from a network of activists in Syria.
Another 42 people, including 11 children, have been killed in strikes on eastern Aleppo.
It reported five more deaths in rebel fire on the Kurdish-majority Sheikh Maqsud district of the city.
The Syrian conflict began as a mostly unarmed uprising against President Bashar al-Assad in March 2011.
However, it quickly escalated into a full-blown civil war, with more than 280,000 people now estimated to have been killed in fighting between the government, the opposition and other armed groups.