Human Rights Watch has denounced the killing of hundreds of pro-Morsi supporters last year.
Tripoli has struggled to rein in warring militia brigades formed after the fall of dictator Muammar Gaddafi.
Lead U.S. negotiator declined to give a final deadline for final nuclear deal.
Move will delay the formation of an urgently needed power-sharing government.
Selection of moderate Sunni Islamist may be first step towards the creation of a coalition government.
Security areas were hit by two successive explosions.
The strike is just the latest challenge faced by the unity government, which is grappling with internal tensions.
The Iraqi prime minister aims to form a new cabinet on time despite an intensifying Sunni insurgency.
Officials say latest extension will allow more time for a finalized agreement.
Maliki's former backers in Tehran and Washington are both supporting his successor Haider al-Abad.
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