"A strong protest has been launched by the Pakistan army and we reserve the right to protect our citizens and soldiers against aggression."
 
The US and Afghan military have not yet responded to the allegations.
 
Afghan operation
 

"There has been anger from the tribal groups [in Pakistan]... They are now saying they will retaliate across the border for the strike"

Kamal Hyder,
Al Jazeera's correspondent in Afghanistan

The Afghan army, backed by the US military, is understood to have entered the area in an attempt to secure the release of seven soldiers held by the Taliban in Pakistan.
 
But Pakistani officials said Afghan forces tried to capture parts of the Soran Dara area, which borders the Afghan province of Nangarhar and which Pakistan claims is its own territory.
 
"There is confusion over what happened," Kamal Hyder, Al Jazeera's correspondent in Islamabad, said.
 
"Officials have confirmed that Pakistani troops were killed … in an area where Americans and Afghans were conducting joint operations."
 
Another Al Jazeera correspondent based in Islamabad said that military sources had told him that a US spy plane was used in the air raid.
 
'Spy plane' spotted

Damagh Khan Mohmand, a local tribesman who witnessed the outbreak of fighting late on Tuesday, said that the clashes lasted for four hours.

He said that Afghan and foreign forces traded fire with both Pakistani tribesmen and troops.

Afghan forces receive training and operational
support from the US-led coalition [AFP]

Two aircraft then bombed several locations, hitting two Frontier Corps posts, Khan Mohmand said.

Hyder said the incident is not the first attack on a Pakistani military post.

"A little over a month ago there was an attack at a post not far from Chopara checkpoint," he said. 

"Al Jazeera sources in Kabul say that the Nato-led coalition is investigating. The coalition has not released any official statements; nor has the Pakistani military.

"There has been anger from the tribal groups, who have an armed group. They are now saying they will retaliate across the border for the strike."

Pakistan's foreign office issued a statement condemning the "senseless use of air power" urging the US-led international force to hand over the  results of its investigation into the incident.
  
"The attack also tends to undermine the very basis of our co-operation with the coalition forces and warrants a serious rethink on their part of the consequences that could ensue from such rash acts," it said.

Border dispute

A series of missile attacks have been attributed to US-led forces in Afghanistan in recent months.

More than a dozen people were killed in one such incident in the tribal region of Bajaur in May.

There have been several disputes over the 2,500km Pakistan-Afghanistan border recently.
 
Both countries, whose governments are both allies of the US in its so-called "war on terror", have also argued over how to tackle fighters loyal to the Taliban.

Foreign forces within the Nato-led coalition and the government in Kabul have alleged that Pakistan is not being tough enough on the opposition fighters.

Pakistan's new government entered peace talks with Taliban loyalists shortly after allies of Pervez Musharraf, Pakistan's president, were beaten in recent elections.