Pakistan's long-running campaign against militants in its tribal regions has led to the arrest of at least 20 senior Islamic State members and hundreds of others, a military spokesman said on Thursday.

‘We have arrested the core of 20-25 militants of Daesh [Islamic State], including its Pakistan chief Hafiz Umer,’ said Lieutenant General Asim Saleem Bajwa in the garrison city of Rawalpindi.

Apart from the leadership of the group, another 309 militants and supporters of Islamic State had been arrested across the country, he said, without elaborating on the time or location of the arrests.

The anti-militant operation, dubbed Zarb-e-Azb (Sword Strike) was billed in June 2014 as a final push against the strongholds of all militant groups.

Islamic State still poses a threat in Pakistan due to its presence on Afghanistan's border, Bajwa said.

Pakistan has faced regular violence from militant Islamic groups for over a decade, killing tens of thousands of people, according to official estimates.

Bajwa said the army would next focus on increasing security along the 2,600-kilometre border with Afghanistan, including setting up 18 regular crossing points, and ‘hundreds’ of security posts.