BEIRUT, Lebanon — Rebel fighters on Monday swept into a sprawling government air base in northern Syria where isolated government troops had fought off their attacks for nearly a year, and by early Tuesday controlled almost all the base, seizing several tanks and other munitions and taking soldiers prisoner, rebel and opposition groups said.

The victory, said by the groups to have been led by two foreign men in an armored vehicle who carried out a suicide attack to breach the defenses of the Minakh air base, was bound to boost the morale of an insurgency that has faltered in recent months with rebels fighting among themselves and losing long-held ground to the army.

Such gains have sometimes been reversed within days, as the government strikes back from the air. But if it holds, the rebels’ seizure of the Minakh base in Aleppo Province will challenge the government’s assertion that it is rolling to victory and demonstrate the complexity of the Syrian battlefield, which neither side has been able to control and where momentum shifts from place to place and week to week.

Even as the battle at Minakh was raging, the government was celebrating its own victory in the central city of Homs, where the defense minister toured the shattered Khalidiyeh neighborhood, long held by insurgents, and posed in front of the Khalid bin al-Waleed mosque — a 13th-century landmark that had been a rebel rallying point and was heavily damaged in the fighting.