LAHORE (Reuters) -- A Pakistani court disqualified former prime minister Nawaz Sharif on Monday from contesting a by-election for a seat in the National Assembly later this week.

Ever since Sharif returned home from eight years in exile last November, he has been crystal clear in his intention to drive his usurper, President Pervez Musharraf, from power.
Sharif was barred from running in a general election in February because he had been convicted for the 1999 hijacking of then army chief Musharraf's plane, an action that triggered the military coup that overthrew him.
Sharif's party was runner up in the February vote to the Pakistan People's Party (PPP) of the late Benazir Bhutto, another former prime minister who returned from exile late last year only to be assassinated in December while campaigning for the poll.
Having trounced the pro-Musharraf parties, the PPP and Sharif's party forged a post-election alliance.
Sharif pulled his ministers out of the cabinet after just six weeks, as Bhutto's husband, Asif Ali Zardari, reneged on a commitment to swiftly reinstate judges Musharraf had dismissed during a brief phase of emergency rule late last year.
While Sharif's party has maintained support for the government, without being part of it, there is speculation that once Musharraf goes the post-election alliance will break completely as Sharif and Zardari will battle for power.
While Sharif has said Musharraf should be impeached or tried for treason, Zardari wants to ease Musharraf out in a less confrontational manner to avoid more upheaval in the country. The PPP has drafted a constitutional package that would take away most of the president's powers.
Uncertainty over Musharraf's position and infighting within the coalition have prolonged the sense of instability that has gripped the nuclear armed nation since Musharraf tried to fire the country's top judge in March, 2007.
That move set in train a series of events that led to the defeat of Musharraf's allies in February and rendered him increasingly isolated and unpopular.
Sharif had been cleared by the Election Commission to contest the by-elections due on Thursday, but on Monday a high court in the eastern city of Lahore again barred him from running.
“The decision is based on a conspiracy. It's a political decision,” Sharif's party spokesman Siddiqul Farooq told Reuters.
A prosecution lawyer said the court did not immediately give any reason for its decision.
Musharraf has so far resisted calls for his resignation, and his fate, along with the related issue of the reinstatement of the judges, has preoccupied a fragile coalition faced with mounting economic difficulties and the threat of violence.
Fears that Pakistan's new civilian leaders will mess up their chance to govern have been reflected in a crisis in investor confidence that has wiped almost 30 percent off share values in the last two months.
On Monday the main Karachi stock index lost 4 percent, hitting the lowest level for more than 15 months.-