Interior minister Nisar Ali Khan had announced last week that military will remain Islamabad from August 1 till October end, under article 245 of the Pakistani constitution.
Article 245 which deals with the functions of the armed forces states says that "armed forces shall, under the directions of the federal government, defend Pakistan against external aggression or threat of war, and, subject to law, act in aid of civil power when called upon to do so".
According to security sources, five companies of army will be deployed primarily to guard key government installations and other sensitive spots, including the woody Margalla Hills National Park.
The government's decision pitted it against the Opposition parties, which termed it as the failure of Nawaz Sharif led civilian government, which took charge last year after the first-ever peaceful democratic transition.
It is feared that the government will expand the deployment and handover the security of other cities to the armed forces.
Key opposition Pakistan People's Party has announced to raise the issue in the parliament on Monday.
The move will give the army control over Islamabad's law and order situation ahead of a key protest march announced by Pakistan Tehreek-e-Insaf chief Imran Khan on August 14.
It is widely believed that the article was invoked to thwart the rally of Khan who had threatened that the march would seal the fate of the PML-N government.
Khan is protesting over the alleged rigging in last year's general election.
After several small rallies during the previous months to force the government for a recount of at least four selected national assembly seats which his party lost in 2013, he gave the call for a major protest in the capital.
Army is a powerful institution and has ruled the country for more than half of its history since Pakistan was created in 1947.
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