Afghanistan's defence ministry said on Sunday its forces killed 28 fighters and wounded 32 others in Nuristan province after a group crossed the border from Pakistan. The ministry said the group included Islamic State militants and that most were former Afghan government security personnel.

According to the ministry, the men crossed into Kamdesh district on Saturday with the intention of carrying out attacks. It alleged Pakistani militias had supported the fighters, and said the survivors retreated toward Pakistani militia positions.

Pakistan's information ministry rejected the claims, calling them "frivolous, baseless and devoid of any truth". It denied that its forces or intelligence agencies were involved in the clashes, had recruited former Afghan personnel, or had facilitated Islamic State fighters.

Reuters said it could not independently verify the Afghan ministry's account or the casualty figures. The claims come days after Pakistan launched airstrikes inside Afghanistan against militants, and exchanges of fire continue along the border.

Tensions are rising along the Durand Line, with troops on both sides on high alert and each capital accusing the other of sheltering attackers.