Fighting between Syrian government forces and rebel groups raged near Aleppo international airport and nearby airbases as the battle for Syria's second city entered its second year, activists said.
"Fierce clashes broke out at dawn near Aleppo international airport and Nairab air base," the UK-based Syrian Observatory for Human Rights said on Sunday.
The monitoring group also reported fighting in the Suleiman Halabi district of the city, once Syria's commercial hub, and overnight clashes at Kwayris military airport.
Violence in Aleppo comes a year after a massive rebel advance into the provincial capital. Stalemate has gripped the city ever since, dividing it into areas under and out of government control.
The pro-regime Al-Watan daily on Sunday lashed out at the Aleppo rebels, saying they "have not succeeded in securing their goal of taking control of Syria's commercial capital".
Elsewhere, the Observatory reported that a Republican Guard officer had been killed by rebels at a key flashpoint.
"Fighting in Adra on the northeastern outskirts of Damascus left an elite Republican Guard officer dead," Observatory director Rami Abdel Rahman told the AFP news agency.
Adra is an entry point to the capital's key Abbasiyeen Square, the target of several rebel attacks in recent months.
State news agency SANA said the army "captured several terrorists from Jabhat al-Nusra, some of them foreign nationals", west of Adra.
Meanwhile, clashes between Kurdish fighters and al-Qaeda-affiliated groups raged in northern Syria, according to Kurdish media in the region.
Kurdish fighters loyal to the Democratic Union Party (PYD) recently expelled fighters allied to Jabhat al-Nusra and the Islamic State of Iraq and the Levant from some of the strategic Kurdish towns in the north.
Kurdish regions have been administered by local Kurdish councils since President Bashar al-Assad's forces withdrew from the areas in mid-2012.
The redeployment was seen as a tactical move by the regime, freeing up forces to battle rebels elsewhere, and encouraging the Kurds to avoid allying with the opposition in order to maintain their new-found autonomy.
Sunday's violence came a day after at least 109 people were killed nationwide, the Observatory said. It estimates a death toll of more than 100,000 people in the 28-month war.