BAGHDAD -- His days in power in Iraq appear increasingly numbered. World leaders, including his biggest ally, Iran, hail the nomination of the man who would be his successor.

There's seemingly little left for Prime Minister Nouri al-Maliki to cling to, beyond the support of party stalwarts and high-ranking loyalists in the military.

Al-Maliki looked even more isolated Tuesday, a day after Iraq's president appointed Haider al-Abadi as prime minister-designate to form a caretaker government -- a move seen as a major step toward breaking the political deadlock that has paralyzed the country since April elections. It also comes after Islamic extremists have swept across northern Iraq, prompting the U.S. to launch airstrikes and directly arm Kurds who are battling the militants.

Despite the backing he enjoys among the top military brass, al-Maliki told the Iraqi army Tuesday to keep out of politics and focus on protecting the nation.

Al-Maliki, who has been in power for eight years, insists he should keep his post as prime minister of the Shiite-led government for a third term because his bloc won the most seats in the assembly, even though he has lost some support with the main coalition of Shiite parties.

U.S. President Barack Obama has called the nomination of al-Abadi a positive step for Iraq, and U.N. Secretary-General Ban Ki-moon said Tuesday he welcomed the formation of a new government "acceptable to all components of Iraqi society."

Saudi Arabia's King Abdullah sent his congratulations. The official Saudi Press Agency said the king expressed his hope the new prime minister, president and parliament speaker would restore cohesion and unity among the Iraqi people. The move represents a sharp pivot from the bitter relationship that Riyadh and Baghdad had under al-Maliki, when each side blamed the other for sectarian strife and fueling extremism.

Even Shiite powerhouse Iran rallied behind al-Abadi as a badly needed unifying figure in the face of the insurgency by the Sunni militants of the Islamic State group. Top Iranian official Ali Shamkhani offered his congratulations to the veteran Iraqi politician, indicating that Tehran, with its considerable influence on the Shiite parties, is further shifting away from al-Maliki.

In remarks to reporters in New York, Ban warned against the Iraqi military taking sides in Iraq.

"It is imperative that the security forces refrain from intervening in the political process," he said.

Since winning his second term in 2010, al-Maliki has worked to craft a military in which the top brass are loyal to him.

During a televised discussion with his senior military commanders, al-Maliki urged the armed forces not to interfere in the political process. Heightened security on Monday sparked concerns in Baghdad and elsewhere in Iraq that security forces might implement a lockdown after President Fouad Massoum appointed al-Abadi.

Al-Maliki himself raised the spectre of further unrest by saying that Sunni militants or Shiite militiamen might don military uniforms and try to take control of the streets on the pretext of supporting him. But he also warned against such actions.

"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 told the senior army and police commanders.

Analysts say the Iraqi armed forces and his remaining political allies prefer to avoid a military confrontation and instead are interested in protecting their own positions.

Hoshyar Zebari, a Kurdish politician who formerly served as foreign minister in al-Maliki's government, said military commanders in Baghdad "have assured the president and prime minister-designate that they will not take sides, that they will abide by the constitution and they will support democratic institutions in the country."

"Also Shiite armed militias made similar pledges that they will not undermine the security of the people," Zebari said.

Austin Long, a member of the Arnold A. Saltzman Institute of War and Peace Studies at Columbia University, said Washington and Tehran should try to ensure that al-Maliki has a "safe exit" from power.

"A lot of people don't want to let go of power because they get a little Messiah complex, but also, they want to be sure that if they peacefully transfer power, then they won't end up swinging from a lamp post," Long said.

U.S. Secretary of State John Kerry urged al-Abadi to work quickly to form an inclusive government and said the U.S. is prepared to offer it significant additional aid in the fight against Islamic State militants.

The U.S. has already increased its role in fighting the Islamic State militant group, which has threatened the autonomous Kurdish region in northern Iraq. The airstrikes, which began Friday, have reinvigorated Iraqi Kurdish forces.

On Tuesday, a U.S. drone destroyed a militant mortar position threatening Kurdish forces defending refugees near the Syrian border.

An Iraqi military helicopter providing aid to civilians fleeing the militants crashed near the Sinjar mountains in northern Iraq, killing the pilot, army spokesman Qassim al-Moussawi said in a statement. The helicopter crashed after too many civilians tried to board it.

The New York Times reported one of its reporters, Alissa J. Rubin, was in the helicopter and suffered an apparent concussion and broken wrists in the crash.

France and Britain stepped up support Tuesday for thousands of people fleeing the Islamic militants in northern Iraq, pledging more air drops, money and equipment to ease suffering and bolster fighters battling the Sunni insurgents.

Britain fast-tracked 3 million pounds ($5 million) in aid. The European Union said it wants to "bring vital assistance to hundreds of thousands of Iraqi civilians trapped by the fighting" and was increasing its aid by 5 million euros ($7 million) for a total of about $23 million this year.

EU Aid Commissioner Kristalina Georgieva said the funding will help "vulnerable Iraqis, including the minority groups besieged in the mountains of Sinjar" and the communities hosting a growing number of refugees.

In other violence reported Tuesday, a car bomb exploded in the Shiite neighbourhood of Zafaraniya, killing four people and wounding 13 others, police said. Another bomb detonated in the commercial district of Karrada, killing eight, according to medical officials in a nearby hospital. All the officials spoke on condition of anonymity because they were not authorized to talk to the media.