FIERCE BATTLES raged yesterday as Afghan troops fought to retake a northern border district from the Taliban.

The fighting over Darqad district in Takhar province — on the border with Tajikistan — came as a Russian intelligence chief warned that Islamic extremists could expand into central Asia.

Taliban spokesman Zabihullah Mujahid emailed media organisations to say the battle for Darqad began at dawn on Wednesday.

He said two Taliban guerillas were killed as the insurgents captured government buildings, including police headquarters.

The provincial governor’s spokesman Sonatullah Taimor said that six members of the security forces had been killed.

Afghan officials have said the Taliban have joined with other insurgents, such as the Islamic Movement of Uzbekistan, and are spreading across the north with the aim of infiltrating central Asian states.

The new alliance briefly captured the prosperous northern city of Kunduz in an audacious surprise attack last month.

Meanwhile, Russian Federal Security Service director Alexander Bortnikov warned of an imminent threat to the former Soviet central Asian republics from an unholy alliance between the Taliban and Islamic State (Isis).

“The escalation of tension in Afghanistan is causing serious concern,” Mr Bortnikov said.

“Numerous Isis gangs that are part of the Taliban movement are currently concentrated on the northern borders of that country.

“Some of them have joined Islamic State, which has dramatically intensified the threat of a terrorist invasion of c entral Asia.”

Earlier this month Russian President Vladimir Putin urged a meeting of the Commonwealth of Independent States to be prepared to repel attacks from Afghanistan.