He said Pakistan, an ally of the United States, had made a "very strong" protest to international forces in Afghanistan.

A spokesman for the Nato-led International Security Assistance Force in Afghanistan said he had no knowledge of any such incident.

'Imminent threat'

However, a spokesman for a separate US-led force said it did fire into Pakistan early on Wednesday in response to a threat.

"Coalition forces did use precision guided munitions in response to an imminent threat from the Haqqani network," said Major Chris Belcher, a military spokesman, referring to fighters loyal to Jalauddin Haqqani and his son Sirajuddin.

"It is not the first time that they [US-led forces] have had to respond to an imminent threat across the border in Pakistan"

Major Chris Belcher, military spokesman
The two Haqqanis, who are allegedly based in the Waziristan town of Miranshah, are said to lead Taliban forces who are battling the Pakistani army in the region.

Belcher said he had no "battle damage assessment", meaning he had no information about casualties or damage.

"The information I have is that the government of Pakistan was notified immediately following the strike," he said.
  
"It is not the first time that they [US-led forces] have had to respond to an imminent threat across the border in Pakistan. Every time we do, we clear that with Pakistani authorities."

Pakistan does not officially allow US forces to enter or attack groups on Pakistani territory despite the heavy fighting on both sides of the border since Taliban forces were forced out of power in Afghanistan in 2001.

However, several previous missile strikes in the region have been attributed to the US, including one that killed Abu Laith al-Libi, a senior al-Qaeda commander, in North Waziristan in January.