Kerry said he was deeply sorry for the incident. "I have 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. He, however, said that Davis enjoyed diplomatic immunity and Pakistani courts had no jurisdiction to try him.

He said Pakistan is a signatory to the Vienna Convention and under the international law Davis will be tried in an American court.

Kerry said, "I am not here to dictate terms. We have to focus on greater issues that relate to Pakistan's stability.”

Kerry said the US respects Pakistan's law and legal system and hope the issue will be resolved soon.

According to sources, Kerry will hold meetings with key figures in Pakistan for Davis’ early release.

Meanwhile, according to Reuters, the Pakistani Taleban warned the government on Tuesday it would oppose any move to release Davis.

“If (Pakistani) rulers hand him over to America then we will target these rulers. If Pakistani courts cannot punish Davis then they should hand him over to us,” said Azam Tariq, spokesman for the Tehrik-e-Taleban Pakistan (Taleban movement of Pakistan).

“We will give exemplary punishment to the killer Davis.”

On Thursday, the United States is expected to present a petition to a Lahore court to certify that Davis has diplomatic immunity and should be released.

The warning from the Al-Qaeda linked Taleban, which has kept up suicide bombings to destabilize Pakistan’s government despite several army offensives, underscores the charged atmosphere surrounding Davis’ case.

Cash-strapped Pakistan, one of the largest non-NATO recipients of American military aid, is loathe to risk losing US support by keeping Davis in jail but also fears antagonizing religious groups who see the government as a US puppet.

Jamaat-e-Islami, a religious and political party capable of organizing large protests, accused the United States of exerting “unprincipled and unlawful” pressure on Pakistan.

“Why is America hell bent on trampling on Pakistani law and its judicial system? We will forcefully protest if he is released without a court order,” Jamaat-e-Islami deputy chief Liaquat Baluch told Reuters.

Religious parties don’t win many votes in elections. But the government can’t afford to ignore the groups who often seize on issues concerning the United States to promote their cause.

“Of course he (Davis) should not be released. He has committed a crime and he should be punished. He doesn’t have immunity,” said Yahya Mujhaid, a spokesman for Jamaat-ud-Dawa, which was blacklisted by the UN over its links to the Lashkar-e-Taiba (LeT) militant group blamed for the 2008 attack on Mumbai. It denies it has links to the LeT.

“If he is released, we will register our protest but in a peaceful way. We will hold rallies ... Not only us, the whole of Pakistan will protest against any such move.”

Some members of the Pakistani media, which has in the past accused US aid workers of being spies, have also called for Davis to be put on trial in Pakistan.

“Davis is not a diplomat but a US spy,” the Taleban spokesman said.

Supporters of the slain men have held protests and burned US flags. In addition to the two men Davis shot, a third man was killed when a US Consulate vehicle, apparently trying to rescue Davis, struck and killed a passerby.

Punjab Law Minister Rana Sanaullah said the provincial government sent the US Consulate reminders that it should hand over the car and the driver who killed the man.