At least seven Pakistani soldiers have been killed in a clash with pro-Taleban militants in a tribal area near the Afghan border, the military says.
Twenty-three tribal militants were also killed in the fighting in Mohmand agency, the army said.
Fighting broke out after militants ambushed the troops, it said.
Attacks by pro-Taleban militants in Pakistan's north-west have soared in the past year, but Mohmand agency has seen relatively little of the violence.
"The militants attacked a security forces convoy and the forces responded with the help of local people, killing 23 of the attackers," military spokesman Maj Gen Waheed Arshad told the AFP news agency.
Reports said the army convoy was travelling to Mohmand's main town of Ghalanai when it came under attack.
Residents said the security forces responded with artillery fire and helicopter gun ships were called in, Reuters news agency reports.
Militancy has spread across north-west Pakistan since last July, when troops stormed the radical Red Mosque in Islamabad to stop armed militants trying to enforce their version of strict Islamic law in the capital.
More than 100 people were killed in the operation.
The pro-Taleban militants said none of their fighters had been killed in the clash in Mohmand.
"We will continue to mount attacks from Swat to Waziristan until the army operation is discontinued, and Maulana Abdul Aziz and his companions are released," a spokesman for the militants told the BBC's Urdu service.
Abdul Aziz was the head cleric of the Red Mosque until being arrested in July.
There have been few reports of clashes to date in Mohmand, which is situated next to another tribal agency Bajaur.
Meanwhile, six Pakistanis working for a Chinese company have been kidnapped in the South Waziristan tribal area further west, reports say.
The Chinese firm is building a dam in South Waziristan but little progress has been made since two Chinese workers were abducted by militants in 2004.
Pakistani security forces freed one of the Chinese men, but the other died in the rescue.
Hundreds of Pakistani troops have been killed in clashes with militants since they were sent into tribal areas bordering Afghanistan after the attacks of 11 September, 2001.
The US and Nato say the border region has become a "safe haven" for al-Qaeda and the Taleban.