A Pakistan court on Thursday put off ruling whether a US official accused of double murder has diplomatic immunity, threatening to prolong a crisis with Washington for another month.

The court adjourned until March 14, prolonging tensions between the United States and Pakistan, where an anti-American population of 167 million is ruled by a weak and unpopular government closely allied in the US war in Afghanistan.

The American, named as Raymond Davis, whom Washington insists has full diplomatic immunity, says he acted in self-defence when he shot dead two men in a busy street in the eastern city of Lahore on January 27.

A third Pakistani died when struck by a US diplomatic vehicle that came to Davis's assistance. The American was then arrested by Pakistani police, who have rubbished his claim of self-defence and accused him of double murder.

"As the deputy attorney general has requested three weeks to submit a reply on the status of Raymond Davis, the case is adjourned until March 14," Lahore high court chief justice Ijaz Mohammad Chaudhry said.

The highest court in Punjab province had already given the foreign ministry 15 days to confirm whether Davis has full diplomatic status — as Washington insists — and is thus immune from trial.

The Pakistan Government is under enormous domestic pressure not to be seen as kow-towing to US demands for his release and has come under fire over how American officials are seemingly free to drive around with loaded weapons.

US President Barack Obama this week demanded the American's release, but the court in Punjab, where the main opposition party at the federal level controls local government, kept his name on the exit control list on Thursday.

Pakistani lawyers who want Davis prosecuted argue that diplomatic immunity should not apply in cases of grave crimes. While shooting someone in self-defence is legal in Pakistan, double murder qualifies as a serious crime.

Many Pakistanis remain suspicious about why Davis, who reportedly worked for a security contractor, was carrying loaded weapons and a GPS satellite tracking device. Neither have US authorities confirmed his name or precise job.

Pakistan's unpopular President Asif Ali Zardari and the Prime Minister Yousuf Raza Gilani, who is struggling to keep his coalition in power, have refused to comment on Davis' status, saying it is up to the courts to decide.

On Wednesday, Gilani even asked Islamic scholars to help, suggesting that the families might pardon the American and telling clerics that the government was caught between a public backlash and international anger.

US Senator John Kerry, who is respected in Pakistan for negotiating a $7.5 billion aid package, made a 24-hour visit to express regret for the killings and promised that Davis would face a criminal investigation at home.

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.

Pakistan is under huge pressure from the United States to do more to root out Afghan Taliban and Al Qaeda-linked militants from its Northwestern region, which borders Afghanistan.

Islamabad denies Persistent Western claims that its intelligence services still collude with Islamist fighters killing US forces in Afghanistan.

Hundreds of Pakistanis have taken to the streets demanding that Davis be hanged over the killings and domestic media has been rife with allegations of a spy conspiracy. The widow of one of the men shot dead has committed suicide.

A court last Friday remanded Davis in custody until February 25.