ISLAMABA: Pakistan's anti-corruption chief refused an order by the country's top court to arrest the prime minister in a graft case on Thursday, saying he did not have sufficient evidence.

The government and the Supreme Court have repeatedly clashed over the last year, and the chief justice's demand on Tuesday that Prime Minister Raja Pervaiz Ashraf be arrested set the stage for a new round of political crisis in Pakistan, a key U.S. ally in the fight against Islamic militants and efforts to stabilize neighboring Afghanistan.

Fasih Bokhari, chief of the National Accountability Bureau, told the Supreme Court that the initial investigation into the case was flawed and that he needed more time to determine whether the prime minister should be arrested.

The case involves kickbacks that Ashraf allegedly took during his time as minister of water and power that were related to private power stations built to provide electricity to energy-starved Pakistan. The prime minister has denied the allegations.

The investigating officers "were not able to bring incriminating evidence but relied on oral statements which are not warranted in the court of law," said Bokhari.

One of the judges, Sheikh Azmat Saeed, chided Bokhari, saying he was acting more like a defense lawyer than a government prosecutor.

Chief Justice Iftikhar Chaudhry questioned why the anti-corruption chief needed more time since the case against the prime minister has been pending for about a year. He ordered Bokhari to bring the case files back to the judges later in the day so they can determine whether there is incriminating evidence.

"There may be some who consider themselves above the law, but let me make it clear there is no one above the law," said the chief justice.