Some 200 militants streamed over the border from Afghanistan and attacked a nearby Pakistani checkpoint on Wednesday, killing at least five security troops, police said.
The incident in Upper Dir district underscores the dangers posed by the porous nature of the Pakistan-Afghanistan border, which both countries have struggled to control as a means of stopping al-Qaida and Taliban-led insurgent movements who have ties on both sides of the boundary.
Also Wednesday, a helicopter carrying a top Pakistani army officer whose responsibilities include overseeing the border with arch-rival India crashed into the Indus River in the eastern Punjab province. Officials said they feared there were no survivors.
The cross-border attack was the latest bloodshed as the Pakistani Taliban and affiliated groups carry out threats to avenge the U.S. raid that killed Osama bin Laden in Pakistan's northwest on May 2. But it was more likely a reaction to ongoing Pakistani military offensives against insurgents along the volatile border.
It was not clear whether the militants were Afghans or Pakistanis. The border area is a global hub for militants, including al-Qaida and allies such as the Pakistani Taliban, who seek to topple the U.S.-backed Islamabad government.
The pre-dawn assault was launched in Shaltalo village in the mountainous northwestern region of Dir and fighting was still continuing, police said according to Reuters.
"They (militants) were in military uniform. They attacked the outpost and then went into forest there," Mahmood Ahmed, a police officer in the region, told Reuters by telephone.
Local police official Bahadur Khan, however, told The Associated Press that Wednesday's attack began around noon.
A shootout was still ongoing an hour later at the scene in Shaltalo, which borders Afghanistan's Kunar province, he said.
Reports of the death toll varied from one to seven. It was not possible to independently verify the conflicting reports.
Army officer in chopper crash
The helicopter crash Wednesday occurred near the town of Kot Sultan Bhakri in Pakistan's Punjab province, which borders India.
Maj. Gen. Mohammed Nawaz, who commanded the paramilitary border guards known as the Punjab Rangers, was in the chopper when it went down in the Indus river, said Mushtaq Anjum, a senior government official.
A military official also confirmed that Nawaz was onboard. He requested anonymity because he was not authorized to speak to media.
It was unclear how many other people were on the aircraft. The reason for the crash was under investigation.
Upper Dir lies just outside of Pakistan's tribal areas, but it, too, has witnessed al-Qaida and Taliban militant activity, and the Pakistani military has carried out operations there in the past. The area is remote and dangerous, making it difficult to independently verify information.
The U.S. has lauded Pakistan's operations against insurgents, which have been carried out primarily in the semi-autonomous tribal areas and targeted militants attacking the Pakistani state.
But Pakistan has, at least publicly so far, resisted American appeals to stage an offensive in the North Waziristan tribal region, the primary haven for militant groups that attack U.S. and NATO forces across the border in Afghanistan.