Javed Hashmi, president of the 15-party Alliance for Restoration of Democracy, was arrested for allegedly releasing an anonymous letter purportedly written by army officials criticising Pakistan President Gen Pervez Musharraf's leadership.
Hashmi has been charged with inciting the armed forces against the government.
Hashmi, a firebrand leader of the Pakistan Muslim League (N), is a close lieutenant of deposed prime minister Nawaz Sharif. He was arrested along with his driver in Islamabad on Wednesday night as he was coming out of the Parliament Lodges (which accommodates lawmakers).
"Javed Hashmi wanted to come out of Parliament Lodges but both entry and exit gates were closed," a PML (N) spokesman told mediapersons alleging that policemen slapped his driver before arresting the two and taking them to an unknown destination.
The official APP news agency, quoting a press note issued by the district magistrate of Islamabad, said the letter called for trial of top army officials for subverting democracy in the country.
"Javed Hashmi has tried in the letter to support India viz a viz Pakistan army, has maligned army personnel and attempted to incite them for mutiny," the note said. An FIR was registered against him based on a complaint by a person named Khursheed Ahmed. He was charged under various sections, which included incitement of armed forces to rebel against the government.
Considering the charges against him, the ARD leader could be tried under the Army Act by a special army tribunal for inciting the army to rebel.
Hashmi had released the anonymous letter in the cafeteria of the parliament house on October 20 claiming to have received it from some men in uniform who did not want to be identified. The letter, though unsigned, is reportedly on the letterhead of the General Headquarters of the Pakistan Army.
Hashmi, perhaps, anticipated his arrest and addressed a press conference on Wednesday stating that opposition leaders receive such letters every day.
He respected the dignity and honour of the armed forces but urged them to pay more attention to defending the country from external forces.
He said the government planned to arrest him on a law coined by the British but vowed to continue his fight for the restoration of democracy.
Sharif, former prime minister Benazir Bhutto, Muthahida Majlis Amal, leader Qazi Hussain Ahmad are among those who have condemned Hashmi's arrest. They said the government was leveling very serious charges against him.
Hashmi, who heads the PML-N in Sharif's absence, was recently elected president of ARD after the death of its leader Nawabzada Nasarullah Khan. PPP leader Amin Fahim was elected as its chairman.
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