Pakistani security forces backed by helicopter gun ships have launched a fresh offensive in the South Waziristan region, officials say.
The army says that the offensive against militants is entering a final stage
Military and transport helicopters are reported to be accompanied by jet fighters west of the town of Wana.
Witnesses say that they heard the helicopters fire rockets at suspected militant hideouts.
An earlier offensive ended on Sunday after attacks using artillery, helicopter gun ships and jet fighters.
Since Sunday there have been at least two incidents of fighting - in one dozens of militants attacked a border security post.
The army has been trying to persuade rebellious sub-tribes protecting several hundred suspected foreign militants to hand them over for registration, so far unsuccessfully.
Instead, the tribesmen have been digging in, staging lightning strikes against the military.
They accuse the security forces of fighting against them on behalf of the Americans who are continuing to mount anti-Taleban operations across the rugged border in Afghanistan.
"It is the continuation of the operation which started last week in response to the attack on our security forces," military spokesman Major-General Shaukat Sultan told the Reuters news agency.
"Wherever we find a hideout or base of militants we will knock it out," he said.
The BBC's Rahimullah Yusufzai in Peshawar says that the latest manoeuvres are highly significant, because they are taking place in the mountainous Angor Adda area - regarded as one of the last strongholds of foreign militants.
He says they will be regarded by the army as the culmination of their ongoing efforts to flush foreign forces out of South Waziristan.
Our correspondent says that the military is also trying to seal most of the South Waziristan's border areas with Afghanistan.
Residents of Angor Adda - 60 kms west of Wana - say that helicopters have been seen since early Thursday morning.
The area is close to fighting which ended on Sunday between security forces and suspected militants.
The Pakistani military says it has destroyed al-Qaeda positions in South Waziristan
Military officials say that finished with at least 72 people dead, including 17 Pakistani soldiers.
In a separate incident early on Thursday morning, militants are reported to have fired three rockets at a Pakistani security post north of Wana. Witnesses say there were no reports of any casualties.
President Musharraf said earlier this year that between 500-600 al-Qaeda members were hiding in the South Waziristan semi-autonomous area.
He has repeatedly pledged not to allow foreign militants to be based in his country.