Aziz's economic reforms have strengthened the economy, but ordinary Pakistanis complain of rising prices and unemployment.

The opposition's main complaint against Aziz, a former finance minister and ex-Citibank executive, is that he was chosen by President Pervez Musharraf, who came to power in a military coup in late 1999 and controversially retains his role as army chief.

The move will be backed by an Islamist alliance, which forms the largest opposition bloc, as well as the mainstream parties of former Prime Ministers Nawaz Sharif and Benazir Bhutto, who are both living in exile.

"We have decided to move the no-trust motion in the National Assembly on August 23," Liaquat Baluch, a leader of the Islamist Muttahida Majlis-e-Amal alliance, told Reuters.

The opposition lacks the necessary seats in the assembly to win a vote, but the move is seen as part of a campaign to keep the government on the defensive ahead of elections due at the end of this year.

"This government has lost confidence of the people on all fronts," Farhatullah Babar, a spokesman for Bhutto's Pakistan Peoples Party said.

"This whole system is planted by General Musharraf to sustain military power and yes, this no-trust is all against General Musharraf."

Musharraf has already said that under the constitution he can be re-elected for a second term of office by the current assembly, before it is dissolved in late 2007.

Bhutto and Sharif in May put aside their differences and vowed to work together by signing a "charter of democracy" in London, and said they would return to Pakistan together before the general election.

Musharraf's current term expires in mid-November next year, as does parliament's.

After the coup, Musharraf was regarded as a pariah in the international community until Washington embraced him as an ally in a war on terrorism following the September 11, 2001, attacks on the United States.