WASHINGTON: The United States has stepped up pressure on Pakistan to free an American accused of murder, warning that high-level dialogue is at risk with the war partner, diplomats said Tuesday.

Secretary of State Hillary Clinton declined to meet Pakistan's Foreign Minister Shah Mehmood Qureshi at a weekend conference in Munich to show displeasure over the case, according to a diplomat familiar with the issue.

US officials have told Pakistan that the case of the imprisoned American “has to be resolved before we can move to a higher level of discussion,” the diplomat told AFP.

US officials said that the United States has not suspended all contact with Pakistan.

“We continue to engage the Pakistani government at the highest levels to seek resolution of this case,” State Department spokesman Philip Crowley told AFP.

“We continue to stress that the US diplomat has diplomatic immunity and should be released,” he said.

Clinton still met in Munich with General Ashfaq Kayani, the head of Pakistan's powerful army, and Pakistani President Asif Ali Zardari held talks on Monday with the US ambassador, Cameron Munter.

The American, identified by Pakistani police as Raymond Davis, was arrested on January 27 after shooting dead two Pakistani motorcyclists.

The American said he shot the men in self-defense, believing they would rob him. A third Pakistani was run over and killed by a US consulate vehicle that had come to assist Davis, according to police.