Iraqi news reports says troops loyal to Prime Minister Nouri al-Maliki have surrounded the home of President Fouad Massoum.
Details were sketchy early Monday, as reports circulated of government troop deployments around Baghdad's so-called Green Zone - the highly protected district that houses Iraq's key institutions.
The deployment came as Maliki - under growing pressure to end his bid for a third term - announced on national television that he is taking legal action against the president for what he called "a clear constitutional violation."
Maliki, whose coalition won the most seats in April elections, claims the president violated the charter by failing to name a new prime minister from the country's largest parliamentary bloc by a Sunday deadline. He accused the president of non-action "for the sake of political goals."
Late Sunday, the State Department voiced full U.S. support for Massoum, who was elected president by parliament late last month.
U.S. officials and many Western analysts say Prime Minister Maliki, a Shi'ite, has failed to unify the divided country since taking office in 2006. They describe him as increasingly unacceptable to Iraq's Sunni Muslims, to Kurds and to many of his fellow Shi'ites.