Afghan troops are seen in the Chardarah district of Kunduz province

Heavy fighting is continuing in the northern Afghan city of Kunduz, a day after government forces launched an attack to reclaim it from the Taliban.

Two US air strikes on Tuesday halted an attempt by insurgents to seize the airport, the army’s stronghold. Afghanistan’s spy agency says the strikes killed the Taliban leader in the province and his deputy, but the Taliban have denied this.

The capture of Kunduz represents the militants’ biggest victory since 2001. Militant violence has increased across Afghanistan since the departure of most Western forces at the end of 2014.

On Tuesday the United States acknowledged the seizure of Kunduz as a setback, but said it remained confident that Afghan security forces could re-take the city.

An unspecified number of NATO special forces have now reached the city, reports say.

Overnight there were clashes around Kunduz, but it remains unclear just how much of it remains under government or Taliban control. (BBC)