By Mubasher Bukhari
LAHORE, Pakistan (Reuters) - A Pakistani election tribunal expelled a senior minister and ally of Prime Minister Nawaz Sharif from parliament on Monday for vote rigging in a 2013 election, a decision the opposition said vindicated its complaints.
Protests last year over cheating in the election, which brought Pakistan's first transition between civilian governments, were led by cricketer-turned-politician Imran Khan and raised fears about stability in the nuclear-armed country.
"It took two years to get a verdict and it has been proved that election staff conducted post-poll rigging," Khan told reporters. "They should be interrogated to know who asked them to do so."
Railways Minister Saad Rafique denied the accusations of irregularities, saying election organizers were responsible and he would challenge the ruling in the Supreme Court.
"The tribunal is punishing my party and my voters for the incompetence of the returning and presiding officers," Rafique told Reuters by telephone.
Rafique is free to run again in a by-election in the constituency in the city of Lahore. A new vote must be held in 60 days, the tribunal said.
The ruling party's main challenger looks set to be Khan's party.
Sharif's Pakistan Muslim League denied Khan's accusations of rigging in 2013. It won the general election with a sizeable majority while Khan's party came third, its best ever showing.
The vote was largely seen as a genuine reflection of the electorate's will but irregularities are common in Pakistani elections.
Last year, Khan organized a sit-in protest in central Islamabad to demand a new election.
The rally turned deadly in September when demonstrators clashed with police near government buildings and embassies and three people were killed. The army helped defuse the standoff.
The Karachi Stock Exchange 100-share index closed slightly lower on late selling triggered by the tribunal's decision, brokers said.
The overseeing judge issued a one-page verdict disqualifying Rafique and calling for a by-election.
In the hearing, the judge castigated election workers and said ballot bags had been opened with a sharp object and records had been tampered with, media reported.
"The court indirectly validated our claim that the rigging was done after the polling," Mian Muhammad Hussain, a lawyer for Imran Khan's candidate in the constituency, told Reuters.
(Writing by Mehreen Zahra-Malik; Editing by Robert Birsel and Ralph Boulton)