"The nomination is illegal and a breach of the constitution. We will go to the federal court to object to the nomination," Hussein al-Maliki said.

Iraqi President Fuad Masum on Monday tasked deputy parliamentary speaker Haidar Abadi with forming a government during a brief ceremony broadcast on state television.

The move, which comes after months of political wrangling, is likely to be resisted by Nuri al-Maliki, who has rejected calls to drop his bid for a third term as prime minister.

This is while the United Nations warned Monday that the Iraqi security forces should not get in the way of the political transition after the president named an alternative to Nuri al-Maliki as prime minister.

"The Iraqi security forces should refrain from actions that may be seen as interference in matters related to the democratic transfer of political authority," top UN envoy in Iraq Nickolay Mladenov said.

Special forces, police and army had deployed around strategic locations in Baghdad late Sunday before Maliki made a desperate last stand on state television, vowing to sue the president for failing to name him as prime minister.

RA/NJF