Pakistani Prime Minister Yousuf Raza Gilani refused Friday to step down from office, a day after the Supreme Court found him guilty of contempt of court for not reopening corruption cases against President Asif Ali Zardari.

Mr. Gilani told parliament Friday that only its lawmakers could remove him from office. He said his only offense was “protecting the constitution.”

The court gave Mr. Gilani only a symbolic sentence of less than a minute's detention, sparing him a possible jail term of up to six months. But the verdict sparked widespread protests across Pakistan Thursday, during which demonstrators chanted and waved his pictures and said it was shameful he had been convicted.

Mr. Gilani's lawyer said his client asked him to appeal the judgment. He said his client was convicted on a charge for which he was never indicted.

The conviction triggered an immediate debate about Mr. Gilani's status as prime minister. Some legal experts say the fact that he was sentenced to a prison term, even for less than a minute, makes him ineligible to sit in parliament for the next five years.

Opposition leaders, including former prime minister Nawaz Sharif, called on Mr. Gilani to step down, saying they will no longer accept him as the country's prime minister.

Thursday's guilty verdict is the latest development in what has been an ongoing battle between the court and the prime minister over the status of corruption cases dating back to the 1990s.

Prosecutors accuse President Zardari, former prime minister Benazir Bhutto and others of laundering millions of dollars through Swiss bank accounts. Ms. Bhutto, President Zardari's wife, was assassinated in 2007.

Charges against Mr. Zardari and the others were dropped after a 2007 amnesty agreement, but the court struck down the deal in 2009 and has been battling to reopen the cases ever since.

Prime Minister Gilani had refused to cooperate, arguing instead that the president has legal immunity while in office and that reopening the cases would be unconstitutional.