Fierce fighting also broke out in the eastern and southern suburbs of the Syrian capital, Damascus, activists and rebel fighters reported.
Islam Alloush, a spokesman for the Jaish al-Islam fighting group, said government forces moved in on the suburb of Mayda, seeking to block a rebel supply line, while the opposition fought back to regain a number of areas previously captured.
The violence came a day after Syrian President Bashar Assad's government announced a three-day truce to coincide with the Muslim holiday of Eid al-Fitr, which marks the end of Ramadan.
The US Secretary of State John Kerry had praised the declaration and said efforts were underway to extend it.
Today, the UN Syria envoy, Staffan de Mistura, noted "initial reports of potential violations" but urged all parties to abide by the truce.
Government forces and allied troops, including Lebanon's Hezbollah militia, have been mounting repeated attacks on the Castello road to close the only route to the opposition-held areas in Aleppo city.
The government offensive secured control over the surrounding Mallah farms, leaving troops less than 1.3 kilometres away from Castello road, the military media arm of Hezbollah said.
In a statement, it said the advance was in retaliation for violations of the truce by armed groups. Syrian State TV declared that, "terrorists are violating the truce."
The rebel group, Nour al-Din Zinky, posted on its Facebook page that government warplanes and artillery heavily shelled the Mallah farms close to the road, and had taken control of some of them in an attempt to cut the rebel supply line.
The Britain-based Syrian Observatory for Human Rights, a monitoring group, said the clashes were reported to the west and east of Castello.
