US Ambassador to Islamabad Anne Patterson offered Washington's "deepest apology" over the killings and violations.
"We extend our deepest apology to Pakistan and the families of the Frontier Scouts who were killed and injured," the ambassador said.
This is while NATO admitted its two helicopters had entered Pakistani airspace. Commander of US and NATO forces in Afghanistan Gen. David Petraeus vowed to work to stop similar incidents happening in the future.
The developments come days after Islamabad closed a major crossing along the border with Afghanistan, in reaction to US-led incursions into its territory.
Islamabad had reportedly stressed that US-led forces should accept responsibility and apologize for their recent violation of Pakistan's airspace.
Experts say the apology can pave the way for Pakistan to reopen a key border-crossing that the US-led military alliance uses to transfer goods into landlocked Afghanistan.
It would also determine if the current strain in Pakistan-US ties caused by repeated violations by NATO helicopters will stop or intensify.
US-led forces have carried out a record number of unauthorized airstrikes in Pakistan in 2010.
Islamabad has condemned the unauthorized US airstrikes, saying such attacks violate Pakistan's sovereignty.
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