"The families of the victims of the January 27 incident in Lahore have pardoned Raymond Davis. I am grateful for their generosity. I wish to express, once again, my regret for the incident," Ambassador Cameron Munter said in a statement released by the State Department.

A US official said Davis was flown out of Pakistan on Wednesday after being acquitted following a deal to pay "blood money" to the victims' families, removing a significant irritant in the already rocky relationship between Washington and Islamabad.

"Davis was released from Pakistani custody and is out of the country. There was no quid pro quo," the official said, speaking on condition of anonymity.

Munter said the US Department of Justice has opened an investigation into the incident involving Davis, who shot dead two Pakistanis in the eastern Punjab city of Lahore on Jan. 27 after what he described as an attempted armed robbery.

Davis said he acted in self-defense and the United States says he had diplomatic immunity and should have been immediately repatriated.

Munter, underscoring his "respect for Pakistan and its people," said the United States remained committed to working with Pakistan "to move ahead in ways that will benefit us all."