The dispute over the arrest of the man has become a crisis in U.S.-Pakistan relations and officials said they feared it could threaten future cooperation in a critical theater of the war against extremists and al-Qaida unless it is resolved quickly. Two top Republicans on the House Armed Services Committee said U.S. aid to Pakistan is in jeopardy if the American is not released.
The detainee case has clouded prospects for three-way strategic talks between Afghanistan, Pakistan and the U.S. that are set for Feb. 24 in Washington.
While officials said the talks are still scheduled, they said the discussions could be postponed or downgraded to a lower level if the case has not been resolved by then.
Washington insists the detained American has diplomatic immunity and shot the Pakistanis in self-defense as they tried to rob him at gunpoint. The U.S. says the man's detention is illegal under international agreements covering diplomatic ties.
"We continue to make clear to the government of Pakistan that our diplomat has diplomatic immunity, in our view was acting in self-defense and should be released," State Department spokesman P.J. Crowley said. "Pakistan should fulfill its international obligations under the Vienna Convention."
Crowley later sent out a Twitter message underscoring that U.S. contacts with Pakistan "express the importance of resolving the case of a U.S. diplomat in accordance with international law."
But Pakistani leaders, facing a groundswell of popular anger triggered by the incident, have avoided definitive statements on the status of the American, whom they have identified as Raymond Davis. Davis' next court appearance is set for Friday.
Pakistani Foreign Ministry spokesman Abdul Basit said the two countries should not let disagreement over the case overshadow the strategic value of a good relationship.
"Our relations are mature enough to navigate through difficulties," he wrote in a text message.
But the U.S. has said it will not let the matter drop, and has been unusually direct in showing its anger at the Pakistani position.
On Capitol Hill, Armed Services Committee Chairman Howard "Buck" McKeon, D-Calif., and Rep. John Kline, R-Minn., said they bluntly told senior Pakistani officials during a recent trip about the ramifications if they continue to detain Davis.
"I think it is imperative that they release him and certainly the possibility that there would be repercussions if they don't," Kline told reporters at a news conference.
The lawmakers suggested that an effort to cut aid to Pakistan might occur when the House considers spending bills in the coming weeks. They said it would garner widespread support because of the outrage over the detention of an American.
Most notably, Secretary of State Hillary Rodham Clinton would not meet Pakistani Foreign Secretary Shah Mahmood Qureshi during an international security conference in Munich, Germany, last weekend.
Under the complex rules of diplomatic protocol, seeing Qureshi, who is Clinton's equal, would have conveyed a message that relations were normal when they were not, officials said.
Qureshi opted not to go the conference. But the officials, who spoke on condition of anonymity because they were not authorized to speak publicly about the matter, could not say whether the hardline U.S. stance was the reason.
Clinton did meet with and raise the Davis case with Pakistan's army chief, Gen. Ashfaq Parvez Kayani, on the sidelines of the Munich conference. The U.S. officials said Clinton went ahead with that meeting because she and the Army chief were not direct counterparts.
The U.S. ambassador to Pakistan, Cameron Munter, also met with Pakistani President Asif Ali Zardari on Monday and pressed him to release Davis. Clinton spoke to Zardari by phone last week on the same matter, and taken together the contacts indicate growing U.S. frustration with an ally considered key to ending the conflict in Afghanistan.
Pakistan risks looking like an American lackey if it caves into demands to free Davis. But it's also a risk to ignore the U.S., which provides it with billions of dollars in military and other aid.
Pakistani officials say Davis' fate is up to courts in Punjab province, while provincial officials say the federal government must inform them whether Davis has immunity and has not done so. The two governments are controlled by rival political parties, which further complicates the matter.
Davis shot the two men Jan. 27 in the eastern city of Lahore. A third Pakistani, a bystander, died when a car rushing to aid Davis struck him. Police have said they want to question the Americans suspected in that death as well.
The wife of one of the men whom Davis shot committed suicide on Sunday, explaining beforehand that she feared her husband's killer would be freed without trial. Her death further inflamed anti-American sentiment.
Toosi reported from Islamabad.
Associated Press writers Riaz Khan and Rasool Dawar in Peshawar, Mohammad Ejaz in Bannu, Hussain Afzal in Parachinar and Donna Cassata in Washington contributed to this report.