KABUL (Reuters) - Heavy fighting between Afghan security forces and Taleban insurgents that killed more than 30 combatants on Monday threatened a major northern city, prompting President Ashraf Ghani to delay a state visit to India.

Officials said hundreds of Taleban insurgents had attacked police and army checkposts in the province of Kunduz, the militants' last stronghold before US coalition forces drove them from power in 2001.

Now they threaten to overrun parts of the provincial capital, after fighting that killed eight Afghan security forces and at least two dozen Taleban in the area, a spokesman for the provincial governor said.

"The threat level is very high, but with new reinforcements, our security forces have gained morale and god willing, we will win the fight," said Abdul Waseh Basel, the spokesman.

The insurgents have overrun seven army and police checkposts in central Kunduz and two districts, Taleban spokesman Zabihullah Mujahid said in an email statement.

Ghani postponed his planned departure for New Delhi and called Nato's General John Campbell to a meeting at the presidential palace to discuss the Kunduz fighting, the general said.

It was unclear how long the delay would be. Ghani's spokesman was not immediately available for comment.

Battles were raging about 6km south of Kunduz city, officials said. Insurgents also broke into the city itself, in the southern district of Gul Tepa, Basel told Reuters.

Afghan security forces used artillery to defend the city, another official said. "The sound of heavy weapons fired by Afghan forces can be heard in the city," said Kunduz police spokesman Sayed Sarwar Hussaini.