Political deadlock has prevented Iraqi politicians from uniting against Islamic State militants whose advance in the north has rattled the Baghdad government and its Western allies.
A senior U.S. official for Iraq said on Sunday he fully supported Iraqi President Fouad Masoum after al-Maliki, who the United States has blamed for stoking Iraq's security crisis, accused Masoum of violating the constitution.
U.S. jet fighters and drones conducted four more airstrikes on ISIS militants in Iraq over the weekend, taking out armoured carriers and a truck that were firing on civilians, as Iraq's human rights minister said ISIS militants killed at least 500 members of the Yazidi ethnic minority.
U.S. Central Command says the strikes were spread out, with three before noon ET on Saturday and one about 3 p.m.
The military says indications suggest that the strikes were successful in destroying the armoured vehicles.
Freelance reporter Hermione Gee told CBC News from Erbil that humanitarian aid was being stepped up, with the U.S., Turkey and the U.K. helping with airdrops on a mountain where tens of thousands of Yazidis have been stranded upon fleeing fighters with ISIS, which also goes by the name the Islamic State.
Asked if the U.S. airstrikes were making a difference for the Yazidis, Gee said one strike overnight at militants in Sinjar who were firing at the group were "taken out," restoring some calm.
Gee said she was with Kurdish forces about 30 kilometres from Erbill on Saturday, and she was told things were "peaceful" following the Thursday and Friday night airstrikes because heavy weaponry operated by ISIS was destroyed.
Buried alive in Sinjar
The international community has expressed concern that the Yazidis trapped on the Sinjar mountain range in northeast Iraq are running out of food and water. Hundreds of women from the minority religious community have already been taken captive by Sunni militants.
On Sunday, Iraqi human rights minister Mohammed Shia al-Sudani told Reuters the Sunni militants had also buried alive some of their victims, including women and children. Some 300 women were kidnapped as slaves, he added.
"We have striking evidence obtained from Yazidis fleeing Sinjar and some who escaped death, and also crime scene images that show indisputably that the gangs of the Islamic States have executed at least 500 Yazidis after seizing Sinjar," Sudani told Reuters.
Sinjar is the ancient home of the Yazidis, one of the towns captured by the Sunni militants who view the community as "devil worshippers."
"Some of the victims, including women and children were buried alive in scattered mass graves in and around Sinjar," Sudani said.
The Islamic State, which has declared a caliphate in parts of Iraq and Syria, has prompted tens of thousands of Yazidis and Christians to flee for their lives during their push to within a 30-minute drive of the Kurdish regional capital Arbil.
The Yazidis, followers of an ancient religion derived from Zoroastrianism, are spread over northern Iraq and are part of the country's Kurdish minority.
A deadline passed at midday on Sunday for 300 Yazidi families to convert to Islam or face death at the hands of ISIS. It was not immediately clear whether the Iraqi minister was talking about the fate of those families or others in the conflict.
The militant group, which arrived in northern Iraq in June, has routed Kurds in its latest advance, seizing several towns, a fifth oilfield and Iraq's biggest dam — possibly gaining the ability to flood cities and cut off water and power supplies.
The Canadian government on Sunday said it is sending an additional $5 million in humanitarian aid to the region — providing food, hygiene kits, cooking materials, blankets and other essentials to those affected by the violence.
The money will also help pay for repairs to water and sanitation facilities.
"Canada continues to stand by the people of Iraq in these difficult times and condemns the terrorist actions of ISIS and the killing of innocent civilians in northern Iraq in the strongest possible terms," Minister of International Development Christian Paradis said in a statement.
"Canada will continue working closely with our allies to determine how we can best continue to support the needs of Iraqi civilians, particularly religious minorities," Paradis said.
Canada has provided over $16 million to respond to humanitarian needs in Iraq, of which $6.8 million was for populations affected by civil unrest and $9.6 million for Syrian refugees, according to the Department of Foreign Affairs.
U.S. President Barack Obama justified the U.S. military's return to fighting in Iraq on Saturday by saying America must act now to prevent genocide, protect its diplomats and provide humanitarian aid to the trapped Yazidi refugees.
"This is going to be a long-term project" that won't end and can't succeed unless Iraqis form an inclusive government in Baghdad capable of keeping the country from breaking apart, Obama said.
But the help comes too late for many of the religious minorities targeted for elimination by the Islamic State group, which swept past U.S.-trained and equipped Iraqi government forces in recent weeks and now controls much of Iraq.
A delayed response by the Shia-led government in Baghdad left Kurdish forces struggling to contain the Sunni extremists' advances.
The UN said more than 500,000 people have been displaced by the violence in Iraq since June, bringing this year's total to well over one million.
Tens of thousands of displaced members of the Yazidi religious minority remain surrounded by ISIS fighters in the Sinjar mountains of northwest Iraq.
The U.S. military said it conducted its third airdrop of food and water for the Yazidis late Saturday.
Three aircraft dropped 72 bundles, containing 3,804 gallons of drinking water and 16,128 meals, U.S. officials said.
They said to date, U.S. military aircraft have delivered more than 52,000 meals and 10,600 gallons of drinking water.