A Pakistani intelligence chief, regarded as a dangerous enemy by assassinated former Prime Minister Benazir Bhutto, will quit his job before her party comes to power at the head of a new coalition.

Bhutto wrote to President Pervez Musharraf before her assassination on December 27, identifying four members of the civilian-military establishment who should be investigated if she was killed.

Ijaz Shah, head of the Intelligence Bureau (IB), one of Pakistan's three security services, was believed to be one of the people Bhutto suspected of conspiring against her.

Bhutto survived a suicide bomb attack during her homecoming procession through Karachi in October to mark the end of more than eight years of self-exile. At least 139 people were killed in the attack.

Shah, a retired army brigadier regarded as close to Musharraf, held a "farewell meeting" with caretaker Prime Minister Mohammadmian Soomro on Monday.

"He sent his resignation several days back. It's been accepted and yesterday he paid a farewell call on the prime minister," a senior government official told Reuters.

The government controls the IB, whereas the Inter Services Intelligence (ISI) and Military Intelligence are part of the army-dominated military.

Many Pakistanis suspect the country's secret services were behind Bhutto's assassination in the garrison town of Rawalpindi, but Musharraf has denied it.

Investigators say Islamist militants operating out of tribal areas where al Qaeda fighters are based killed Bhutto, who had spoken out more forcibly against the militants than Musharraf's allies had done.

The intelligence agencies have long held influence over politics in Pakistan, two-time prime minister Bhutto had often accused them of destabilising her governments in the late 1980s and 1990s.

The defeat of pro-Musharraf allies in a February 18 election has left the president isolated, and there are moves afoot in the new parliament to bring back judges who Musharraf had deposed last November, when he invoked emergency rule for six weeks.

The newly elected National Assembly dominated by Musharraf's opponents was sworn in on Monday.

The PPP and its partners plan to pass a resolution within 30 days of the formation of their government to bring about the restoration of the judges Musharraf fired.

The president purged the Supreme Court in November out of fear that the judges would rule that his re-election a month earlier was unconstitutional. He has now packed the court with more pliant judges who he hopes will protect him.