Hundreds of Taliban fighters launched an early morning attack Monday on a strategic northern city, storming it from several directions, Afghan officials said.

Sayed Sarwar Hussaini, spokesman for the provincial police chief of Kunduz, said the attack on the city of Kunduz started about 3 a.m. Battles with government forces were still underway in at least four locations, he said.

Taliban spokesman Zabihullah Mujahid claimed responsibility for the attack on his Twitter account, saying the Taliban were entering hospitals around the city hunting for wounded government troops. He advised residents to remain indoors.

Abdul Wadood Wahidi, spokesman for the governor of Kunduz province, said no government buildings, including hospitals, had been overtaken by the insurgents. When the attack started, he said, insurgents had overrun "two local police check points outside the city but have been pushed back from both."

He said three police officers had been wounded, and "more than 20 bodies of Taliban fighters are on the battlefield."

"They are not in a position to take control of the city," Wahidi said of the insurgents. "They have already been defeated by the security forces."

He added that reinforcements from neighboring provinces had already arrived in Kunduz city, with more on the way from other cities, including the capital Kabul and Mazar-i-Sharif.

Mohammad Yusouf Ayubi, the head of the Kunduz provincial council, said city residents were "greatly concerned" about the situation. "The Taliban are trying to take control of Kunduz city and this is why they have launched their attacks from different directions using their full power," he said.

Hussaini said the insurgents had been pushed back from the city and Afghan army helicopters were conducting patrols. "Intensive battles are going on between both the Afghan forces and the insurgents," he said.

Kunduz province is on a strategic crossroads connecting the four points of Afghanistan. It has been the scene of intense insurgent attacks since April, and this is at least the second time the Taliban have attempted to overrun the city.

Afghan officials say the Taliban have joined forces across northern Afghanistan with other regional insurgent groups as they have spread their fight against the government to the previously peaceful region.

The strategy for this year's offensive appears to have been to force government troops to spread resources around the country as the Taliban take control of remote rural districts, even if only temporarily.

However Afghan forces, fighting alone for the first time since the withdrawal of international combat troops last year, have largely held their ground while taking heavy casualties.