Government troops killed at least 75 rebels in and around the Syrian capital on Sunday, the Observatory said.
The rebel capture of the strategic village of Khan al-Assal and two smaller villages was a rare victory in recent months.
Khan al-Assal has been a major front in the fight for Aleppo. In March, chemical weapons were allegedly used in the village, killing more than 30 people. The Syrian government and the rebels blame each other for the attack.
Opposition fighters on Monday took control of the villages on the southwestern outskirts of Aleppo, though clashes were still going on near Khan al-Assal. Inside Aleppo, airstrikes targeted several rebel-held districts, said the Observatory, an anti-regime activists group that relies on reports from activists on the ground.
The opposition's Aleppo Media Center said several rebel factions are taking part in the operation that aims to cut government supply lines to the southern areas of Aleppo province. The AMC said rebels cut the road, but the Observatory said fighting was still in progress there.
Regime forces have been relying on the road to bring supplies and food to government-controlled areas in the north after rebels cut the main highway between Damascus and Aleppo, Syria's largest city, last year.
The Observatory said 14 government troops were killed Monday in the fighting in Aleppo province.
Fighting also raged in Homs, Syria's third largest city, where the regime has been trying to oust rebels from the city center in an offensive that started in late June. Monday's clashes concentrated on the rebel-held Khaldiyeh district, the Observatory said.
Rockets fired by government troops on Khaldiyeh hit the historic Khalid Ibn al-Walid mosque, damaging the tomb of a revered figure in Sunni Islam inside the mosque.
"This is the first time they hit the tomb," said Homs-based activist who identified himself only as Abu Bilal for fear of government reprisals. "Ten rockets hit the mosque today," he said.
An amateur video posted online showed heavy damage in the mosque, including a hole in one of its nine domes. The fence around the tomb was blown away and debris was scattered all over the mosque.
The video appeared genuine and corresponded to other AP reporting on the events depicted.
Diplomatic efforts to solve the crisis sputtered along on Monday.
In Moscow, Syrian Deputy Prime Minister Qadri Jamil told reporters after meeting Russian Foreign Minister Sergey Lavrov that they discussed a possible Russian loan. Jamil did not give details. His comments came after the Syrian pound hit a record low against the U.S. dollar, crossing the 300-pound line, compared with 47 pounds to the dollar at the start of the crisis 29 months ago.
"I hope a decision on offering Syria another loan will be made by the year's end," Jamil said.
Lavrov said the opposition, including the Western-backed Syrian National Coalition, is showing no interest in peace talks to end the civil war, while the Syrian government has said it would take part.
"To our great regret, unlike the government of Syria, a significant part of the opposition, including the National Coalition, aren't showing such readiness," Lavrov said at the start of the talks. "We are persistently and continuously asking our partners, who have a serious influence with the National Coalition, to use it for positive ends and persuade it to revise its current unconstructive stance."
The opposition insists that Assad must step down as the first step in any diplomatic process. Assad insists he can run for president again next year.
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Associated Press writer Vladimir Isachenkov contributed to this report from Moscow.
