Taliban fighters have seized dozens of districts in Afghanistan as they step up attacks during the final withdrawal by foreign troops, the UN has warned, BBC reports. 

The insurgents have taken more than 50 of 370 districts since May, UN special envoy Deborah Lyons told the Security Council, warning of "dire scenarios".

She said increased conflict "means increased insecurity for many other countries, near and far".

The US and Nato are still aiming for a complete troop pullout by 11 September.

However, the Pentagon has said the pace of the withdrawal could change in light of recent Taliban gains.

The hardline Islamist group's recent advances were the result of an "intensified military campaign", Ms Lyons told the the 15-member UN Security Council in New York.

"Those districts that have been taken surround provincial capitals, suggesting that the Taliban are positioning themselves to try and take these capitals once foreign forces are fully withdrawn."

The Taliban also captured Afghanistan's main border crossing with Tajikistan on Tuesday, officials said. The crossing stands in the northern province of Kunduz, where fighting has escalated in recent days.