Rebel fighters killed at least three Pakistani soldiers and injured two others in an attack on a border post in the northwestern tribal belt, officials say.
About two dozen fighters crossed from the Afghan province of Kunar to launch Saturday's pre-dawn ambush in Bajaur district, Pakistani officials said.
"Militants from across the border ambushed a checkpoint. Two security personnel and an officer embraced martyrdom in the attack," a security official in Bajaur told the AFP news agency.
A senior government official said the rebels were forced to flee after troops retaliated.
No group has yet claimed responsibility but both officials said that Pakistani Taliban fighters were involved in the attack.
"It might be in retaliation for the Pakistan military offensive in North Waziristan," the government official told AFP.
Vehicle hit by rocket
A senior military official in Peshawar, the region's main city, told AFP that the troops were killed when a rocket hit a vehicle near the border post.
Maulana Fazlullah, the current head of the Pakistan Taliban, is believed to be hiding across the border in Kunar.
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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 fighters have used to launch attacks.
The army says it has killed 400 fighters in the course of the operation there.
In a statement from Islamabad, the government's Foreign Office said" "Pakistan strongly condemns the terrorist attack on a Bajaur Scouts vehicle at Ghakki Pass in Bajaur Agency today, launched from across the border in Afghanistan.
"An officer and two soldiers embraced shahaadat in the attack, while two soldiers were critically injured.
"A strong protest has been lodged with the Afghan side in Islamabad and Kabul. It has been reiterated that Afghanistan should eliminate the terrorist sanctuaries and not allow its territory to be used against Pakistan."
'Hideouts bombed' in Mir Ali
In another development, a Pakistan military statement said on Saturday, fighter jets bombed hideouts in the town of Mir Ali after attackers fired rockets at a security checkpost, "killing at least 13 militants and destroying seven hideouts".
"A huge cache of arms and ammunition was also destroyed. Most of the terrorists killed in strikes are foreigners," it said.
It said two explosives-laden vehicles were destroyed by air strikes while two suicide bombers blew themselves up when encircled.
More than 400 fighters and 20 soldiers have been killed in the offensive so far, according to the military.
The area is off-limits to journalists and the number and identity of the dead is impossible to verify.
The rugged mountainous area has for years been a hideout for fighters of all stripes - including al-Qaeda and the homegrown Pakistani Taliban as well as foreign fighters including Uzbeks and Uighurs.