ISLAMABAD, Pakistan - Pakistan's Supreme Court decided on Thursday to charge the country's prime minister with contempt for his failure to reopen an old corruption case against the president, a move that could oust the premier from office and land him in prison if he is convicted.

That could create political turmoil within Pakistan, the last thing the government needs as it struggles to deal with an ailing economy, a violent Islamist insurgency and troubled relations with its most important ally, the United States.

The US is likely watching the case closely since it wants Pakistan to focus on pushing the Taliban to make peace with the Afghan government so that Washington can withdraw its troops without a civil war breaking out in the country.

The Supreme Court ordered the government two years ago to write to Swiss authorities requesting they reopen the graft case against President Asif Ali Zardari, which dates to the late 1990s. But the government refused, claiming the president enjoys immunity from prosecution while in office.

Judges ramped up pressure over the case in early January when it threatened to hold Prime Minister Yousuf Raza Gilani in contempt if he didn't write the letter, and ordered him to make a rare appearance before the court to plead his case.

Tension seemed to ease after Gilani struck a conciliatory tone during his appearance before the judges on Jan 19, and his lawyer, Aitzaz Ahsan, agreed to argue the issue of the president's immunity when the hearing resumed. The government previously insisted presidential immunity was a right, and therefore didn't need to be debated in court.

But Ahsan appeared to do a U-turn during the hearings that resumed on Wednesday, refusing to specifically address the issue of presidential immunity. Instead, he simply argued that Gilani should not be held in contempt because his lawyers advised him he did not have to send the letter.

The court said it would officially issue the charges against Gilani when it resumed hearing the case on Feb 13.

Ahsan said he would advise Gilani to appeal the charge.

A defendant has the right to appeal in a contempt case in Pakistan even before a trial begins.

Government supporters have claimed the court is using the case in an attempt to get Zardari out of office because of enmity between the president and the chief justice.

The Supreme Court has also ordered an inquiry into a secret memo scandal that threatens Zardari. The memo was allegedly sent to Washington by the government last year asking for help in stopping a supposed military coup. The government has denied the allegations, and the case appeared to lose steam last week when the main witness refused to come to Pakistan to testify.

The graft case against Zardari relates to kickbacks that he and his late wife, former prime minister Benazir Bhutto, allegedly received from Swiss companies. They were found guilty in absentia in a Swiss court in 2003. Zardari appealed, but Swiss prosecutors ended up dropping the case after the Pakistani parliament passed a bill giving the president and others immunity from old corruption cases.

The Pakistani Supreme Court ruled the bill unconstitutional in 2009 and ordered the government to write to Swiss authorities to reopen the case.