The Pakistani army has killed at least 20 militants in a clash along the Afghan border, military officials say.
The troops were responding to a rocket attack on checkpoints
The fighting began near Wana in South Waziristan after a rocket attack early on Wednesday on two military checkpoints.
The army has reported some casualties but has given no details of its losses.
Tribal militias in the area have been under pressure to either capture and hand over militants or face another Pakistani military offensive.
The fighting came a day after authorities demanded local tribes hand over four people accused of harbouring al-Qaeda militants.
More than 100 people were killed in South Waziristan in March during a Pakistani operation to flush out militants.
Brigadier Mahmood Shah, chief of security for Pakistan's tribal area, said the militants were "definitely foreigners" and one had been captured alive.
Army spokesman Maj Gen Shaukat Sultan said three bodies had been recovered from the fighting in the village of Shakai and they "appeared to be foreigners".
"They are using mortars, heavy machine guns and rockets. We are also using heavy weapons," Brigadier Shah told the private Geo television channel.
The fighting began after rockets were fired at checkpoints near Wana.
Brigadier Shah said Pakistani soldiers were then deployed in an area covering 15 kilometres (10 miles) between the two
The BBC's Paul Anderson in Islamabad says that the military authorities believe several hundred foreign militants are hiding in Pakistan's tribal belt, and are contemplating renewed operations to flush them out.
The army decided to co-opt the tribesmen and their leaders after the failure of a huge operation in March, in which more than 120 people were killed, many of them soldiers.
A 4,000-strong tribal militia has been organised and has been searching the area this week for militants.
But our correspondent says this approach appears to have failed, and there are signs the army is running out of patience.
Residents in Wana have detected a build-up of troops and supplies recently.
President Pervez Musharraf has threatened renewed force if an economic blockade, imposed last week in Wana, fails to force tribesmen to hand over foreigners for registration.
Our correspondent say that the next stage in the coercive process may be the demolition of tribesmen's shops and businesses.