ISLAMABAD, Pakistan — The simmering crisis between Pakistan’s government and judiciary flared dramatically on Thursday when the Supreme Court announced it would pursue contempt charges against the prime minister, Yousaf Raza Gilani, for failing to reopen a corruption investigation into the finances of his boss, President Asif Ali Zardari.

The Supreme Court said it would start proceedings for contempt of court against Mr. Gilani on Feb. 13. If convicted, he faces up to six months in jail and possible disqualification from public office.

The court order was a significant escalation of long-simmering tensions between the judiciary and the government and threatened to plunge the country into fresh political turmoil as its leaders debated the contours of a new strategic relationship with the United States.

Since 2009, the Supreme Court, led by Chief Justice Iftikhar Muhammad Chaudhry, has insisted that the government write a letter to the authorities in Switzerland, asking them to reopen a corruption investigation against Mr. Zardari that stretches back to the 1990s and involves his finances in that country.