US senator John Kerry has voiced regret for the killings of two Pakistanis by an American embassy official as he visited Lahore to resolve a bitter diplomatic row over the man's fate.
Kerry reiterated Washington's stance that the man should be freed under diplomatic immunity and told reporters in the eastern city of Lahore Tuesday that the United States would conduct its own investigation into the killings.
"I want to come here to express our deepest regret for those tragic events and to express the sorrow of American people for the loss of life that has taken place," he said.
"I've come here to listen. I haven't come here to order anybody to do anything; I haven't come here to dictate."
Detained official Raymond Davis insists he acted in self-defence when he shot dead two Pakistanis in Lahore on January 27. A third Pakistani died when struck by a US diplomatic vehicle that came to Davis' assistance.
As Kerry arrived in Lahore, US President Barack Obama weighed in on the spat, insisting that Davis enjoyed diplomatic immunity under the Vienna Conventions.
"We're going to be continuing to work with the Pakistani government to get this person released," Obama said.
"Obviously, we're concerned about the loss of life. We're not callous about that, but there is a broader principle at stake."
The president said diplomatic immunity was critical because otherwise diplomats who "deliver tough messages to countries where we disagree with them" will "start being vulnerable to prosecution locally."
"That's untenable. It means they can't do their job," Obama said.
Many Pakistanis remain suspicious about Davis, who was arrested with loaded weapons and a GPS satellite tracking device, and who police have said is guilty of murder.
US authorities have been vague as to his role in Pakistan, while the fragile but vital alliance between Washington and Islamabad has spun into crisis since Davis was taken into custody.
Kerry, the chairman of the Senate Foreign Relations Committee who helped spearhead a record $7.5 billion aid package for Pakistan, is well respected in the nuclear-armed country on the front line of the US-led war on Al-Qaeda.
His message was more circumspect as he sought to reassure Pakistanis by announcing that the United States would launch its own probe into the affair.
"I can give you the assurance that our Department of Justice will conduct a criminal investigation... and let that facts speak for themselves," he said.
"Let's work together as two countries which have a huge common interest, who are working together toward the same goal and find a path forward."
Pakistan has insisted the case should be dealt with by its courts, with the Lahore high court expected to reconvene on Thursday after giving the foreign ministry 15 days to answer on whether Davis has diplomatic immunity.
A US official told AFP on condition of anonymity that Kerry's mission was not to secure Davis' immediate release but to repair the bruised relationship between his country and Pakistan.
"Pakistani officials have already indicated that Mr. Davis will remain in custody in the near term (but) ...certainly the Davis case will be a topic of discussion and Chairman Kerry's goal is to help tone down the rhetoric and reaffirm our partnership with Pakistan," the official said.
Pakistan's weak and unpopular government has been under enormous pressure to put Davis on trial in a country awash with anti-American sentiment.
The United States has postponed a round of high-level talks with Afghanistan and Pakistan following failed attempts to get Davis out, and US lawmakers have threatened to cut payments to Pakistan unless he is freed.
A court last Friday remanded Davis in custody until February 25 and police accused him of murder.
Hundreds of Pakistanis have taken to the streets demanding that Davis be hanged over the killings. The widow of one of the two men shot dead has also committed suicide.