Troops loyal to Iraqi Prime Minister Nuri al-Maliki have been deployed to strategic locations in Baghdad, after he criticized the president in a surprise speech.
Unidentified officials said the security forces took up positions at key entrances to the capital late on August 10.
Several streets were reportedly closed, as well as some key bridges.
Earlier, Maliki appeared on television saying he intended to file a complaint against President Fuad Masum for committing "a clear constitutional violation."
Maliki, whose coalition won the most seats in April elections, accused the newly elected Kurdish president of failing to name a prime minister.
The United States later threw its weight behind Masum, with Deputy Assistant Secretary of State for Near Eastern Affairs Brett McGurk saying on Twitter that he was “guarantor of the Constitution and a [prime minister] nominee who can build a national consensus."
Maliki is seeking a third term as prime minister, but the rapid advance of Islamist militants in western and northern Iraq during the summer has prompted calls for him to step aside.
Critics accuse Maliki of pursuing a sectarian agenda, which has sidelined Sunni Arabs.
In another development, the leader of Iraq's autonomous Kurdish region appealed on August 10 for international military aid to help defeat Islamic State (IS) fighters.
Masud Barzani's plea came as the U.S. military launched a fourth round of air strikes targeting the militants near the regional capital, Irbil.
Meanwhile, the State Department said it had relocated a limited number of staff members from the U.S. Consulate in Irbil.
Kurdish forces said they had regained control of two towns in Nineveh Province, Gwer and Makhmur, following heavy fighting.
It is the first time Peshmerga forces have regained ground from the IS since U.S. President Barack Obama authorized the air strikes on August 7.
Also on August 10, Britain and France took steps to provide humanitarian aid to thousands of displaced civilians besieged by IS fighters on a mountain in northern Iraq for the past week.
