Iraqi troops imposed heightened security in Baghdad Wednesday as international support mounted for a new prime minister to replace Nouri al-Maliki, who has called on the armed forces to stay out of politics amid fears of a possible coup.

Tanks and Humvees were positioned on Baghdad bridges and at major intersections on Wednesday, with security personnel more visible than usual. About 100 pro-Maliki demonstrators took to Firdous Square in the capital, pledging their allegiance to him.

The embattled premier has grown increasingly isolated, with Iraqi politicians and much of the international community lining up behind Haider al-Abadi, a fellow member of his Shiite Dawa party tasked by the president with forming a new government that can unite the country in the face of an onslaught by Sunni militants.

Widespread discontent with al-Maliki's divisive rule has reached the point where both Saudi Arabia and Iran -- regional rivals often bitterly divided over Iraq -- have expressed support for al-Abadi. The United States, the European Union and the United Nations have also expressed support for new leadership.

But al-Maliki, whose bloc won the most votes in April elections, has thus far refused to step aside and rejected the appointment of al-Abadi as unconstitutional. Al-Abadi was selected by the main Shiite alliance which includes al-Maliki's bloc, but the Islamic Dawa party says al-Abadi "only represents himself."

Tanks and Humvees first rolled across the city early Monday after al-Maliki delivered a surprise midnight address to the nation vowing legal action against President Fouad Massoum for carrying out "a coup against the constitution and the political process."

At a meeting between al-Maliki and senior military commanders broadcast on state television Tuesday, al-Maliki said security forces should not get involved in politics, but raised the specter of further unrest by saying that Sunni militants or Shiite militiamen might don military uniforms and try to take control of the streets.

"This is not allowed because those people, wearing army uniforms and in military vehicles, might take advantage of the situation and move around and make things worse," he said.

The turmoil stems from the rapid advance of the Islamic State group and allied Sunni militants across northern and western Iraq in June. Fueled by widespread Sunni discontent with al-Maliki's rule, the insurgency seized Iraq's second largest city Mosul and routed the beleaguered armed forces. Thousands of people have been killed and more than 1.5 million displaced by the violence.

The militant advance slowed as they approached Baghdad and other majority Shiite areas, but the capital still sees near daily attacks.

A car bomb struck a police a checkpoint in western Baghdad on Wednesday, killing six people, including four policemen, and wounding 16, police and hospital officials said. A separate car bomb killed three people and wounded five others in the Baiyaa neighborhood, and a mortar attack north of the capital killed four and wounded seven, the officials said. They spoke on condition of anonymity because they were not authorized to speak to reporters.

In northern Iraq, thousands of members of the Yazidi religious minority remain stranded in the mountains outside the town of Sinjar, which the Islamic State group captured earlier this month. The Islamic extremists view the Yazidis as apostates and have vowed to kill all those who do not convert.

The Yazidis' plight has prompted a multinational relief effort, with Iraqi and U.S. planes dropping dozens of crates of food and water. An Iraqi helicopter providing aid crashed near the mountain on Tuesday, killing the pilot, army spokesman Qassim al-Moussawi said in a statement. A New York Times reporter and a freelance photographer survived the crash.

The U.S. military has meanwhile targeted the Islamic State group with a series of airstrikes aimed at protecting the Yazidis and slowing the advance of the militants toward Irbil, the capital of the largely autonomous Kurdish region. On Tuesday, a U.S. drone destroyed a militant mortar position threatening Kurdish forces defending refugees near the Syrian border.

Another 130 U.S. troops arrived in Irbil on Tuesday on what the Pentagon described as a temporary mission to assess the scope of the humanitarian crisis on Sinjar Mountain.

Australia's Prime Minister Tony Abbott meanwhile held open the possibility of sending a combat forces to Iraq in addition to military transport aircraft. But Defense Minister David Johnston on Wednesday played down the prospect of an Australian combat force, saying the military had only committed to sending two C-130 Hercules transport planes for humanitarian aid drops to begin within two or three days.