Fighting raged on Sunday close to Aleppo international airport and nearby air bases as the battle for Syria's second city entered its second year, a monitoring group said.
"Fierce clashes broke out at dawn near Aleppo international airport and Nairab air base," said the Syrian Observatory for Human Rights, also reporting fighting in the Suleiman Halabi district of the city.
The violence in Aleppo comes a year after a massive rebel advance into the provincial capital.
Stalemate has gripped the city ever since, splitting it into rebel-held and government-controlled areas.
Rebels have penetrated the regime-held Rashidin district of New Aleppo in a bid to break the stalemate.
While covering the clashes there, an activist working with the Observatory was hit by gunfire from a regime loyalist, said the group.
The pro-regime Al-Watan daily on Sunday said the Aleppo rebels had failed "to secure their goal of taking control of Syria's commercial capital".
Over the past year, insurgents have fought to take Aleppo's airports, aiming to stop regime warplanes from bombing rebel areas.
The city's international airport has been closed since January.
Tens of thousands of Aleppo residents have fled the fighting which has badly damaged one of the Middle East's richest cities in terms of culture and history.
Parts of the ancient souks in the heart of Aleppo were destroyed by fire last September.
In April, the minaret of the famed and ancient Umayyad mosque, an archaeological treasure in Aleppo's UNESCO-listed Old City, was blasted apart.
As with other attacks in the spiralling conflict, the government blamed jihadists, while the opposition charged the army was at fault.
Elsewhere, the Observatory reported that a Republican Guard officer was killed by rebels at a key flashpoint on Sunday.
"Fighting in Adra on the northeastern outskirts of Damascus left an elite Republican Guard officer dead," Observatory director Rami Abdel Rahman told AFP.
Adra is an entry point to the capital's Abbasiyeen Square, the target of several insurgent attacks in recent months.
State news agency SANA said the army "captured several terrorists from (the Islamist) Al-Nusra Front, some of them foreign nationals," west of Adra.
In the coastal town of Bayda, scene of a massacre in May, three men from the same family were executed by regime forces after a night of clashes between rebels and troops, according to the Britain-based Observatory.
Sunday's violence comes a day after at least 109 people died in violence nationwide, said the Observatory which estimates a total death toll of more than 100,000 people in the 28-month war.
Short link: