Image copyright Getty Images Image caption Mr Nabil has been in the post for about five years

The head of Afghanistan intelligence service, Rahmatullah Nabil, has resigned citing "pressures from President Ashraf Ghani".

There has been "repeated verbal demands about my removal from the post," he said in a letter to the president.

It comes a day after the Taliban killed at least 50 people including soldiers in a siege at Kandahar airport.

Mr Nabil and the president differ on Pakistan's role in fighting the militants, says the BBC's Dawood Azami.

Afghan officials often accuse neighbouring Pakistan of supporting Taliban activities in their country.

On Wednesday, Mr Ghani asked Islamabad to help broker peace negotiations with the insurgents during a regional peace conference in the country.

In a Facebook post on Tuesday, Mr Nabil doubted the positive outcome of President Ghani's visit to Pakistan and lashed out at Afghanistan's neighbour for "harbouring and supporting terrorism".

There have been reports that since President Ghani came to power last year, he has sidelined the intelligence chief over his stance on the government's policy towards its neighbour.

Image copyright Reuters Image caption The attack in Kandahar lasted for more than 24 hours

Mr Nabil had been heading the National Directorate of Security (NDS), for about five years.

He was briefly sacked in 2012 by former President Hamid Karzai before he was reinstated.

However, some are blaming him for recent escalation in Taliban attacks in the country, including the brief seizure of northern city of Kunduz in September.

Correspondents say the attacks in Kandahar and Kunduz have exposed a huge failure by the Afghan security forces.