By Kay Johnson

NEW DEHLI (Reuters) -- Afghan government forces recaptured main areas of the northern city of Kunduz from the Taliban in a large offensive in the early hours of Thursday morning, two government officials said.

Details of the operation and which areas were under government control were not immediately clear.

"Afghan security forces got control of Kunduz city from Taliban overnight after heavy fighting," Hamdullah Danishi, acting governor of Kunduz, told Reuters by telephone.

"After we got reinforcement and started a massive operation inside Kunduz city Taliban could not resist and escaped. ... We will give a full report soon," he added.

Interior Minister spokesman Sediq Sediqqi said on Twitter:

"It is retaken and being cleared from terrorists, heavy casualty to the enemy."

The Taliban captured Kunduz, the first provincial capital to fall to the insurgents since they were driven from power in 2001, on Monday. Afghan forces, backed by U.S. air strikes, had been struggling for two days to retake the city.

(Additional reporting by Frank Jack Daniel; Editing by Rachel Armstrong)