The fighting around the suburb of Nayrab, southeast of Aleppo, Syria's largest city and commercial hub, included shelling by Syrian ground-attack aircraft, opposition forces said.
The battle brought opposition Free Syrian Army forces, who are strong in an area east of the city, to within 3 miles of a regime military base at the airport, activists said.
The base is widely used by the regime to bomb rebel-held areas.
Syrian regime or media had no immediate comments or reports on the fighting. The rebel accounts could not be independently confirmed.
The latest fighting came a day after 67 people were killed in Aleppo, the opposition Local Coordination Committees said.
The dead included four Syrian Armenians killed in an ambush as the people drove home from the airport, the committees said.
It also came a day after a car bomb exploded killing 18 regime soldiers in the northwestern FSA stronghold city of Saraqeb, east of Idlib, the British-based Syrian Observatory for Human Rights said.
The soldiers were part of a group of more than 70, the opposition rights group said.
Near Hama, in west-central Syria, two children were among 11 people executed by regime forces after being arrested while they worked on farmland, the Local Coordination Committees said.
All told, 173 people were killed in Syria Wednesday, including 10 children and six women, the committees said. Thirty people died in aerial shelling, it said.
The fighting raged as envoy Lakhdar Brahimi prepared to meet with Assad Thursday in Brahimi's first official visit to Syria.
Brahimi, who met with exiled opposition leaders in Cairo Wednesday, replaces former envoy Kofi Annan, who resigned Aug. 2 in frustration over his inability to persuade Assad and the opposition to halt the conflict, now in its 18th month.
U.N. Secretary-General Ban Ki-moon said Tuesday, "We should not be overly pessimistic" about the international community's determination to resolve the conflict.
European Union foreign policy chief Catherine Ashton said the world was at an impasse over Syria.
Brahimi, a former Algerian foreign minister who has worked for the United Nations in other trouble spots, including Afghanistan and Iraq, is a member of The Elders, an independent group of noted world leaders and elder statesmen working for global peace and human rights. The group, brought together by former South African President and Nobel Peace laureate Nelson Mandela, is led by Nobel Peace laureate Archbishop Desmond Tutu.