Ahead of a crucial Parliament session, Pakistan's ruling coalition on Monday said it has drawn up an 'unimpeachable' chargesheet against President Pervez Musharraf [Images], who has refused to resign despite mounting pressure to do so.

The National Assembly, or lower House of Parliament, was due to convene later in the day -- also Musharraf's 65th birthday.

Officials said charges against the President are likely to be filed later in the week.

Pakistan People's Party spokesman Farhatullah Babar, a member of the committee that is drafting the chargesheet, said the panel had made 'significant progress' in listing the charges against Musharraf, including those of misconduct and violation of the Constitution.

"It will be an unimpeachable document supported by documentary evidence of all the acts of omission and commission committed by Musharraf that make him liable to impeachment several times," Babar said.

Several leaders of the PPP and its ally PML-N had earlier also said the chargesheet would include charges of misconduct and violation of the Constitution. PPP Chairman Asif Ali Zardari's allegation against Musharraf that he 'misappropriated' some $700 million of US aid could also be part of the chargesheet.

Babar said the coalition had uncovered evidence of 'horrendous' crimes allegedly committed during the beleaguered President's rule. He did not elaborate.

"We are in the government now and have access to many previously confidential documents. After going through these documents, we are surprised over the horrendous nature of the crimes committed by President Musharraf during his almost nine-year rule," he said, without commenting on reports that the charges included corruption and murder.