Taliban fighters overran three provincial capitals including the strategic northeastern city of Kunduz on Sunday, local officials said, as the insurgents intensified pressure on the north and threatened further cities.

The insurgents have taken dozens of districts and border crossings in recent months and put pressure on several provincial capitals, including Herat in the west and Kandahar in the south, as foreign troops withdraw.

The offensive has gathered momentum in recent days after the United States announced it would end its military mission in the country by the end of August.

Taliban fighters seized key government buildings in Kunduz, leaving government forces hanging onto control of the airport and their base, a provincial assembly lawmaker said on Sunday, raising fears it could be the latest to fall to the Taliban.

The city of 270,000, is regarded as a strategic prize as it lies at the gateway to mineral-rich Northern provinces and Central Asia.

"Heavy clashes started yesterday afternoon. All government headquarters are in control of the Taliban, only the army base and the airport is with ANDSF (Afghan security forces) from where they are resisting the Taliban," the lawmaker, Amruddin Wali, said.

A security forces spokesman said on Sunday evening that government forces would launch a large scale operation to retake lost areas of the province as soon as possible.

Taliban spokesman Zabihullah Mujahid said the group had largely captured the province and were close to the airport.

Health officials in Kunduz said that 14 bodies, including those of women and children, and more than 30 injured people had been taken to hospital.

The Taliban have also taken government buildings in the northern provincial capital of Sar-e Pul, driving officials out of the main city to a nearby military base, Mohammad Noor Rahmani, a provincial council member of Sar-e Pul province, said.

On Friday, they captured their first provincial capital in years when they took control of Zaranj, on the border with Iran in Afghanistan's southern Nimroz province.

In recent days they have escalated attacks on Northern provinces, which lie outside their traditional strongholds in the south but where the group has been quickly taking ground, often along the border of Afghanistan's Central Asian neighbours and trading partners Turkmenistan, Tajikistan and Uzbekistan.

On Sunday evening, Ashraf Ayni, a representative in parliament for Takhar province, said its capital Taloqan had fallen to the Taliban who had freed prisoners and taken control of all government buildings, driving officials to a nearby district.

On Saturday, heavy fighting took place in Sheberghan, the capital of northern Jawzjan province. The Taliban said they had captured the entire province.

Jawzjan provincial council member Shir Mohammad said most of Sheberghan, including provincial government buildings, had fallen to the Taliban. An Afghan security forces spokesman on Saturday had denied the Taliban had taken the city, saying forces were working to defend Sheberghan without causing civilian casualties. On Sunday, he did not immediately respond to a request for comment for an update on the situation.