Baghdad, Iraq (CNN) -- More than a million Iraqis have been forced from their homes by conflict this year, the U.N. refugee agency said Friday -- a number only likely to rise as Islamist militants and Iraqi security forces battle for control.
A humanitarian crisis is brewing, as families who've fled fighting with little more than the clothes on their back seek water, food and shelter from the summer heat.
Meanwhile, the first of up to 300 U.S. military advisers will arrive in Iraq as soon as Saturday, a senior defense official told CNN. This first group is expected to be very small, the official said.
In addition, some U.S. military personnel already in Iraq at the security cooperation office in the U.S. Embassy in Baghdad may be reassigned to work with them. Those already in Iraq could begin working immediately.
Concern for the soaring number of people displaced in Iraq comes as the UNHCR marks World Refugee Day on Friday. Its report, based on data up to the end of 2013, finds that the number of refugees, asylum seekers and internally displaced people worldwide has, for the first time since World War II, exceeded 50 million people.
Now the crisis in Iraq -- which was already sheltering hundreds of thousands displaced by the war in Syria -- is swelling that number even further.
An estimated 500,000 people fled Iraq's second-largest city, Mosul, last week after it fell to fighters from the Islamic State in Syria and Iraq.
Already, a half-million were displaced from Iraq's western Anbar province, where the Sunni militants have been dominant since early this year.
Added to that are tens of thousands more who have fled their homes in Diyala and Salaheddin governorates amid the recent violence, UNHCR spokeswoman Ariane Rummery told CNN.
Will the number soar still higher? "In terms of the number of displaced people, that really depends on what happens," Rummery said. "But what we know is that conflict and violence fuel displacement.
"With the humanitarian situation, we know that there's a million people displaced and it's not always easy to get to all of them."
While some fleeing families have taken rooms in overcrowded hotels, others, low on funds, have had to take shelter in transit camps that have sprung up near checkpoints controlling entry to Iraq's Kurdish-controlled north.
Those who have fled to the Kurdish region are easier to reach, Rummery said, but others have sought safety in less accessible regions.
U.N. High Commissioner for Refugees Antonio Guterres, speaking in Beirut, warned that any mass exodus of refugees from Iraq could be hard to cope with, given the regional situation. "I hope that this outflow will never come because the capacity of the region to deal with it is practically nonexistent," he said.
Jacqueline Badcock, U.N. humanitarian coordinator for Iraq, said agencies were moving fast to try to meet the needs of Iraq's newly displaced population, despite the volatile situation.
"Food, water, tents and other essential supplies are reaching families in need, additional staff are being mobilized, and emergency funds are being released," she said. "I remind all parties to the conflict that they must allow unfettered and sustained humanitarian access to all people in need."
For days, the United States has considered what to do about the militants, and on Thursday, U.S. President Barack Obama said he was prepared to send as many as 300 military advisers to Iraq, adding that America was not returning to a combat role in the country.
The Pentagon earlier presented Obama with a plan to send up to 100 special forces advisers to Iraq to work along with that country's military, several U.S. officials told CNN on Thursday.
The first group of advisers arriving as early as Saturday will begin work by conducting an initial assessment of Iraqi troop capabilities and on what may be needed for a larger group of U.S. advisers, including additional security measures where they may be deployed, a senior defense official said Friday.
The Pentagon has identified two preliminary locations in Baghdad and northern Iraq for proposed joint Iraq-U.S. operations centers, but those locations are not being disclosed at this point because of security concerns, the official said.
The U.S. withdrew its final troops from Iraq at the end of 2011, nearly nine years after leading the invasion that toppled longtime leader Saddam Hussein.
Putin backs government
As ISIS, born from an al Qaeda splinter group and supported by many Sunni factions, continues its fierce advance in Iraq, senior U.S. officials tell CNN that the Obama administration is of the belief that Prime Minister Nuri al-Maliki is not the leader Iraq needs to unify the country and end sectarian tensions.
The Prime Minister's Shiite-dominated government is accused of fostering sectarian tensions by marginalizing Iraq's Sunni Arab and Kurd minorities.
The officials, along with Arab diplomats, say the White House is now focused on a political transition that would move Iraqis toward a more inclusive government -- one without al-Maliki that would include Sunni, Shiite and Kurdish factions.
Russia, however, expressed its support to the Iraqi government when al-Maliki received a phone call from President Vladimir Putin, the media center for the Iraqi government said Friday.
The leaders discussed the situation in Iraq, and Putin backed the Iraqi government's fight against terrorist groups, according to the Iraqi government.
Top cleric urges all Iraqis to unite against ISIS
Al-Maliki has called for Iraqis to join the military's fight against the Sunni extremists -- a call echoed a week ago in a message from Ayatollah Ali Sistani, the most powerful Shiite cleric in Iraq.
But a senior religious Shia cleric clarified Friday that the top Iraqi Shiite leader was calling for all sects to stand together against ISIS, and not for the country's Shiites to take up arms in a new militia force.
The government should ban all militias and armed groups other than Iraq's security forces, Imam Sayid Ahmed Al-Safi said at Friday prayers in Karbala.
Additionally, he said Iraqis should respect the timeline set by the high court to name the new presidential Cabinet and ministerial positions, following recent elections. Al-Maliki's party came out on top in the balloting, but many in Iraq do not want to see him continue as Prime Minister.
Al-Safi also urged Iraqis not to engage in price gouging. The cost of essentials such as food and cooking gas has soared in recent days, adding to people's anger.
Iraq's military is also calling for retired aircraft technicians, mechanics and officers to re-enroll for active service, the Ministry of Defense announced Friday. They will get their old titles and salaries back.
Meanwhile, what purported to be a slick, English-language propaganda and recruitment video for ISIS was posted to YouTube on Thursday, appealing for Western jihadists to join the militant group. CNN cannot independently confirm the authenticity of the video.
Precious seats on flights
The ISIS fighters, who have vowed to take the capital, have come within 40 miles (64 kilometers) of Baghdad with their assault on the town of Baquba.
The sense of fear was palpable Thursday at Baghdad International Airport, where hundreds of people waited in long security and check-in lines for one of the few, precious seats available on flights out of the capital.
Many people are seeking safety in Iraq's Kurdish-controlled north, particularly Irbil, or in the southern port city of Basra. Others are trying to leave the country altogether.
To accommodate the exodus, airlines have begun adding flights and, in some cases, much larger planes. Still, there are few seats available as most flights, according to travel agencies, are sold out weeks in advance.
Where once there was one Iraqi Airways flight a day to the northern city of Irbil, there are now three.
Amid growing unease, Australia's Defense Department said a small military contingent had been deployed to help protect the Australian Embassy in Baghdad.
Fighting has focused this week on Baiji, where Iraq's largest oil refinery is located.
Neither side is in control of the complex, which refines much of the fuel needed for internal consumption. There are already long lines at many gas stations across the country.
Fighting was also ongoing Friday in the northwestern city of Tal Afar.
In the town of Al-Azzi, militants believed to be ISIS fighters attacked a security post, wounding soldiers and police.
And in Diyala province near Muqdadiya, Shiite militiamen joined security forces in fighting off attacks on predominantly Shiite areas. The militiamen had recently taken over security in some parts of Muqdadiya, according to police in nearby Baquba and Baghdad. The government recently opened a recruiting station in Muqdadiya for volunteers to join the military to fight ISIS.
Also on Thursday, ISIS militants took control of a facility that Saddam Hussein once used to produce and store chemical weapons.
But the State Department doubts that the Al Muthanna complex contains any material of "military value."
"The materials in the bunkers, which date from the 1980s, are of little military value and would be very difficult to safely move," State Department spokeswoman Jen Psaki said Thursday. But "the materials pose serious health hazards to anyone attempting to access the bunkers."