Militants killed at least three Pakistani soldiers in an attack early Saturday on a border post in the restive northwestern tribal belt, officials said.
Around two dozen militants armed with sophisticated weapons crossed from the Afghan province of Kunar to launch the pre-dawn ambush in Bajaur district, Pakistani officials said.
"Militants from across the border ambushed a check post. Two security personnel and an officer embraced martyrdom in the attack," a security official in Bajaur told AFP by telephone.
A senior government official said the militants were forced to flee after troops retaliated.
No group has yet claimed responsibility but both officials said Tehreek-e-Taliban Pakistan (TTP) militants were involved in the attack.
"It might be in retaliation for the Pakistan military offensive in North Waziristan," the government official told AFP.
A senior military official in Peshawar, the region's main city, confirmed the attack and death toll and told AFP that the troops were killed when a rocket hit a vehicle near the check post.
"Two soldiers were wounded and taken to the main hospital in Bajaur," he said.
Hardline cleric Maulana Fazlullah, current head of the TTP which rose up against the Pakistani state in 2007, is believed to be possibly hiding across the border in Kunar.
Pakistan's armed forces have been waging a massive offensive in North Waziristan, a tribal district south of Bajaur, for the past three-and-a-half weeks to eradicate hideouts militants have used to launch attacks across the restive nuclear-armed country.
The army says it has killed 400 insurgents in the course of the operation there.
Another security official in Peshawar told AFP on Saturday that ground troops were pounding militants hideouts with artillery and mortars in the mountainous Dehgan area, some 25 kilometres (16 miles) west of Miranshah, the main town of North Waziristan.
"At least four compounds used by foreign fighters have been destroyed, we are also receiving reports of casualties," the official said.
The rugged mountainous area has for years been a hideout for Islamist militants of all stripes -- including Al-Qaeda and the homegrown TTP as well as foreign fighters including Uzbeks and Uighurs.