The exodus from the mountainous North Waziristan district on the Afghan border began in late May following Pakistani air strikes, locals have told AFP.
But it has been hastened by the Talibans all-night siege of Karachi airport this week, which all but destroyed a tentative peace process.
On Wednesday night two US drone strikes hit the region killing at least 16 in the first such attack this year, fuelling suspicion of coordination between the two countries, with Islamabads patience for talks seemingly exhausted.
But as pressure builds for a fuller response to the airport assault, which was joined by militants from Uzbekistan, residents and officials in the districts main town of Miranshah said the majority of foreign and local fighters had already left.
"Most of them have gone deep into the mountains towards the Afghan border," a senior security official told AFP.
The locals said militant groups were also seen escaping from villages that are a known hub of the dreaded Haqqani network, an Al-Qaeda affiliate known for its spectacular attacks against US forces in Afghanistan.
Rumours of a ground offensive in North Waziristan, one of seven tribal regions along the border, have abounded for years.
But authorities have held back from a final push -- possibly fearing the blowback in Pakistans major cities such as Karachi, where 38 people including 10 militants were killed at the airport.
However, the sheer numbers of people leaving -- some 60,000, according to official estimates, since late May -- suggest that this time might be different.
Editor: Ella Syafputri
Copyright © ANTARA 2014
