Obama to Pakistan: Release Held American At Once

President Barack Obama says an American diplomat detained in Pakistan must be released at once.

The president cited the global system of diplomatic immunity in the case of Raymond Allen Davis, who has been held by Pakistani authorities since he fatally shot two Pakistanis in the eastern city of Lahore on Jan. 27.

"If they (diplomats) start being vulnerable to prosecution, that's untenable," Obama said at a news conference.

The U.S. says Davis, a former Special Forces soldier and an embassy worker, shot in self-defense when two armed men on a motorcycle tried to rob him and that his detention is illegal under international agreements covering diplomats.

Pakistani officials, fearful of a backlash in a population where anti-American fervor is widespread, have avoided verifying his diplomatic status and have referred the case to the courts. Police are pushing for murder charges against the 36-year-old Davis.

U.S. officials have threatened to withhold billions of dollars in aid to Pakistan unless Davis is freed.

Foreign Secretary Salman Bashir issued the warning as the dispute between the two countries over the man's fate reached new levels. In an apparent step to show its displeasure, the United States on Saturday postponed a meeting with Pakistani officials to discuss the war in Afghanistan that was to be held later this month.

Bashir acknowledged that the Washington meetings will likely have to be rescheduled because of the Davis case. The sessions, to be held during the week of Feb. 20, would have included Secretary of State Hillary Rodham Clinton and senior Pakistani and Afghan diplomats.

He noted that the U.S. and Pakistan have a long history, and said it is "unthinkable" that one incident should strain the relationship. Still, he said, "Any U.S. pressure on the issue of Raymond Davis will be counterproductive."

Meanwhile, Pakistan's Islamic hardliners on Tuesday threatened to forcefully block any attempt by their government to hand Davis over, CBS News' Farhan Bokhari reports.

The threat came ahead of Sen. John Kerry's planned arrival in Islamabad amid expectations by Pakistani officials that the visit was aimed at discussing ways to resolve the dispute surrounding Davis - considered a bona fide diplomat by the U.S., and from Washington's perspective, armed with immunity from prosecution. But Pakistan argues Davis was not serving as a diplomat and therefore could not be considered immune from prosecution.

"If Raymond Davis is let go, the responsibility for the consequences of his release will lie with the Pakistani government. We will be compelled to seek revenge," said the Taliban in a message delivered to officials in the country's Khyber-Pakhtunkhwa province along the Afghan border, according to the security official who spoke to CBS News on condition of anonymity.

In Islamabad, Pakistan's capital city, protesters from the Jamaat-e-Islami - the main Islamic political group - gathered in a central part of town to protest against Davis.

"Down with America. Raymond Davis is a murderer and he must face justice," said Saeed Khattak, a young student activist from the Jamaat-e-Islami. In the aftermath of the Davis case, some of the strongest expressions of anti-U.S. sentiment have been seen on the streets of Pakistan - a country which is supposedly a U.S. ally in the war on terror. However, the danger of a fierce backlash from Islamists has put the government of President Asif Ali Zardari on the defensive.

Davis' next hearing is scheduled for Feb. 25.