Major-General Asif Ghafoor told reporters that the operation dubbed Khyber-4 has been tasked with eliminating militant hideouts from an area of about 250-square kilometers in the Rajgal valley. He said militants linked to pro-IS groups, Jamaatul Ahrar and Lashkar-e-Jhangvi, as well as the Pakistani Taliban are entrenched there.
"Presence of Daesh is increasing [in areas opposite to Rajgal across the border in Afghanistan], necessitating this operation to eliminate influence of Daesh being exported to Pakistan through Rajgal valley," asserted Ghafoor, using the Arabic acronym for Islamic State.
The army spokesman underscored challenges the terrain is expected of pose on Pakistani troops, saying the valley consists of eight passes and houses mountain peaks with ranges up to 4,200 meters.
FILE - A Pakistani border security guard stands alert at Pakistan-Afghanistan border post, Chaman in Pakistan, May 5, 2017.
Thousands of troops are participating in the operation and they will be assisted by the Pakistani air force, he added. The general noted that investigators working on recent deadly bombings in Pakistani border areas have also traced back their links to IS' Afghan bases.
General Ghafoor said the military informed its Afghan counterparts and the NATO-led Resolute Support mission in advance about launching of Sunday's operation so they could enhance deployment on their side to prevent fleeing terrorists from entering Afghanistan.
The eastern Afghan province of Nangarhar borders the Rajgal valley.
The U.S. military in partnership with Afghan forces has been conducting major ground operations, backed by airstrikes, against IS bases in volatile the districts of Nangarhar and the adjoining Afghan province of Kunar.
A U.S airstrike in Kunar earlier this week killed the chief of Islamic State in Afghanistan, Abu Sayed. He was the third head of the terrorist group the U.S. military has eliminated in the past year.
Meanwhile, General Ghafoor said fencing the entire 2,600-kilometer border with Afghanistan and construction of outposts as well as forts is underway to effectively guard the largely porous frontier against terrorist infiltration.
Pakistan says the fence is necessary in part because of a lack of cooperation from authorities in Kabul. The border region has long been a source of instability, with militant groups, terrorists and smugglers using the remote, mountainous terrain as cover.
Ghafoor again rejected charges his country is harboring anti-Afghanistan militants, including the dreaded Haqqani network.
'Pakistan has undertaken operations [on its soil] against terrorists of all hues and color, including Haqqanis,' he reiterated.