WASHINGTON -- Asked about Kurdistan in Iraq, the autonomous region that has become the United States' favored partner on the ground against the Islamic State group, most officials and analysts speak of constant attacks, military strategy and weapons supplies.

But what's less discussed is the humanitarian crisis that Iraqi Kurds face because their region has absorbed more than 1 million refugees from Iraq and Syria who fled the extremists. This means that amid its existential battle, Kurdistan is struggling with a question that has plagued other humanitarian havens around the world: Can a government under pressure accommodate all the new arrivals?

Kurdistan's challenge is especially important. Observers agree that eventual victory against the Islamic State and stability in fractured Iraq are impossible if specific communities within the country continue to feel alienated.

Kurdistan's treatment of two groups of refugees -- Sunni Arabs and Kurdish followers of the Yazidi faith -- has come under scrutiny in the past few months. The Huffington Post discussed the communities' concerns in May with Bayan Sami Abdul Rahman, the Iraqi Kurds' top representative in the U.S. Rahman acknowledged isolated difficulties, but said most refugees -- both Sunni Arab and Yazidi Kurds -- were grateful for her regional government's assistance.

The Sunni Arabs -- of whom there are now 800,000 in Iraqi Kurdistan, according to Rahman -- are the primary concern. It was Sunni Arabs' discontent with the Shiite-run central Iraqi government in Baghdad that initially fomented the Sunni extremist Islamic State's growth in Iraq. Many Sunnis, including disenfranchised former supporters of the Saddam Hussein regime, welcomed the militant group as a powerful potential representative of their interests, though it's been as brutal to potential Sunni rivals as it has to its other opponents. The Islamic State's strongholds in Iraq are now largely in Sunni Arab areas, and the militants last month captured the provincial capital of Iraq's Sunni-dominated Anbar province.

Courting Sunni resistance to the Islamic State, or ISIS, is a priority for the U.S. and the Iraqi government. On Wednesday, the White House announced that it would be sending 450 additional advisors to Iraq to run a new U.S. training camp focused on anti-Islamic State Sunni forces. But building trust among Sunnis has been difficult, as Baghdad has worked closely with Shiite militias said to have brutalized Sunni villages after retaking them from ISIS.

So it was all the more dramatic when, in February, Human Rights Watch said ethnically motivated discrimination against Sunnis in Iraq -- which violates international law and could boost ISIS recruitment -- was rampant in Kurdistan.

"Iraqi Kurdish forces have confined thousands of Arabs in 'security zones," Human Rights Watch said in a Feb. 26 statement about its investigation into abuse in Iraqi Kurdistan. "Kurdish forces for months barred Arabs displaced by fighting from returning to their homes in portions of Ninewa and Erbil provinces, while permitting Kurds to return to those areas and even to move into homes of Arabs who fled."

The group said Kurdish security forces and refugees in the region told its investigators Arabs were being kept away from their homes because of a fear that they would help ISIS.

The U.S. and other countries arming the Iraqi Kurdish forces should make clear that they wont stand for discrimination under the guise of countering terrorism," said Letta Tayler, a senior Human Rights Watch terrorism researcher.

Human Rights Watch said the Kurdistan government had eased some restrictions and reaffirmed its commitment to human rights after being approached by the group. Speaking with The Huffington Post, Rahman noted the compassion displayed by Kurds in helping shelter Sunni Arabs -- despite the community's previous connection to the viciously anti-Kurdish Saddam Hussein. But she also conceded there "may have been tensions" because of Kurdistan's security concerns.

"We're at war. We're at war against a terrorist organization that is trying to destabilize the safe areas of Kurdistan region. We have to protect our citizens, the displaced Iraqis. ... We share a 1050-kilometer border with ISIS and they attack us all the time," Rahman said. "Even though we have liberated those areas, they constantly attack the frontline and they constantly test our security forces, so we have to be very careful."

Rahman added that Sunni Arabs had shocked Kurds in August 2014, when some of them joined ISIS in its assault on the Yazidi minority in northwestern Iraq.

"There will be tensions, but the vast majority feel safe and appreciate the support of the Kurdistan Regional Government," Rahman said.

Rahman disputed Human Rights Watch criticism of her region's government, suggesting that the group had not fully accounted for Kurdish worries. "When we talk to Human Rights Watch privately, they understand that, and then when we read their report, it says something else," she said.

Joe Stork, deputy director of Human Rights Watch's Middle East and North Africa division, told HuffPost in a June 4 interview that he felt his group's report had reflected the Kurdish response.

"We stand by our findings," Stork said. "They raised these concerns. We understand that these are their concerns, but we still take the view in many cases these policies were too broad."

Kurdistan's approach shows how deeply suspicious other Iraqi communities have become of the Sunni Arabs -- and how the stigma may complicate any future end to sectarianism and ethnic friction. More examples pop up by the day: interviewed by The New York Times on Tuesday about an ISIS attack in an Anbar Province city, a local elected official blamed gunmen hidden among Sunni Arab refugees.

Discontent among another group of refugees -- the Yazidis from Mount Sinjar -- adds to the difficulties in Iraqi Kurdistan. Though the Yazidis are ethnically Kurdish, some among them have criticized the Kurdistan government for two connected reasons: the belief that Iraqi Kurdistan's forces reacted too slowly to the ISIS advance on Yazidi areas in August, and the feeling that they are politically marginalized in their new temporary home.

Kurdish fighters from Turkey and Syria , who are more leftist than the Iraqi Kurds and are linked to the Kurdish militant movement known as the PKK, are credited by some Yazidis as their true saviors.

Rahman made a frank public admission that the Iraqi Kurdish forces -- hailed as heroes in the West -- could have done better.

"There was disappointment at the beginning with the performance of some of the peshmerga in Sinjar, and there were failures, you know, we're not denying that," Rahman said. "But we were taken by surprise we were shocked at the size and the weaponry and the speed with which ISIS struck.

"I don't want to defend what happened in the early days, but what I can say it that we are absolutely committed to the well-being of the Yazidi community."

Some Yazidis have said that even after they got to safety, they have faced persecution when they have tried to assert their rights -- particularly when they have attempted to establish political or military organizations of their own that have been linked to outside actors that Iraqi Kurdistan mistrusts, namely the Turkish Kurds and the central Baghdad government.

Rahman said she believes that view is not shared by the majority of Yazidis. Most of them, she said, "feel that we are all part of the same fight.

"That doesn't mean that there aren't people who disagree with that and they're welcome to their opinions and we are happy to have discussions with them."