LAHORE, Pakistan - Pakistan's Election Commission on Monday barred former prime minister and opposition leader Nawaz Sharif from a January 8 general election because of his criminal record.

"His nomination papers are rejected because of his convictions," presiding election official Raja Qamaruzaman told Reuters in the eastern city of Lahore, Sharif's power base where last week he registered to run in the election.

The two-time prime minister says the convictions secured against him in the wake of his 1999 ouster by the then army chief, Pervez Musharraf, were politically motivated.

Sharif, who returned from seven years of exile on November 25, has been threatening to boycott the election but he had lodged nomination papers.

His exclusion from the vote will be seen by the opposition as the result of pressure on election officials by President Musharraf to block the old rival he ousted. Critics say Musharraf has sway over voting officials.

"I'm very clear that there is somebody else who is manoeuvring things," said one of Sharif's lawyers, Imtiaz Kaifi. Kaifi said Sharif's party would decide whether to appeal.

"This shows the election is based on rigging. General Musharraf can't face Mr Sharif in the polling that's why he has been denied to contest the election," said a party spokesman, Ahsan Iqbal.

Sharif was not immediately available for comment.

He arrived in Islamabad earlier on Monday for talks with another opposition leader and former prime minister, Benazir Bhutto, on his plan to boycott the vote.

Bhutto, who returned from eight years in self-exile in October, says her party will take part in the election although she has left open the option of joining Sharif in a boycott.

Sharif was convicted of hijacking and terrorism and sentenced to life in prison in 2000 for trying to turn away an aircraft carrying Musharraf, the then military chief whom Sharif had just dismissed, back from an overseas visit in October 1999.

The incident precipitated Musharraf's coup against Sharif.

In July 2000, he was convicted on a corruption charge. He was sent into exile in Saudi Arabia later that year on condition, the government says, that he stay out of politics for 10 years.

Election officials citing financial irregularities last week barred Sharif's brother, Shahbaz, from running.