U.S. intelligence chiefs have repeated their assessment that Iraq and Syria may have been permanently fractured by war and sectarian strife and may not survive as nation-states.

Lieutenant General Vincent Stewart, the head of the Defense Intelligence Agency, repeated his belief that Iraq will break up into three different regions -- Kurdish, Sunni, and Shi'ite -- using the same frank analysis that drew a rebuke from the Iraqi prime minister earlier this summer.

"I'm having a tough time seeing it come back together," he told an industry conference in Washington on September 10, noting that large swaths of both Iraq and Syria have been seized by the Islamic State (IS) group.

IS militants have taken over what roughly might be described as the Sunni third of Iraq in the country's north and west, while taking over about a third of eastern Syria, declaring a radical Sunni Muslim caliphate that spans the border between the two countries.

Meanwhile, Iraqi Kurds, in their semiautonomous region in northern Iraq, have been at the front lines trying to liberate parts of their territory as well as Sunni strongholds in northern Iraq from IS.

Kurdish region President Masud Barzani recently asserted that the Kurds should not have to cede back to the central government territory that Kurds lost lives to free.

"Iraq is obviously falling apart," Barzani told CNN's Christiane Amanpour in an interview in June. "And it’s obvious that the federal or central government has lost control over everything. Everything is collapsing – the army, the troops, the police."

"We did not cause the collapse of Iraq. It is others who did. And we cannot remain hostages for the unknown," he said through an interpreter. "The time is here for the Kurdistan people to determine their future."

In light of IS's foothold in northern Iraq and Barzani's ambitions, Stewart said, "I'm wrestling with the idea that the Kurds will come back to a central government of Iraq."

Similarly, he said, "I can see a time in the future where Syria is fractured into two or three parts."

That is not the U.S. goal, he said, but it's looking increasingly likely.

Lost Control

His remarks were largely affirmed by CIA Director John Brennan, who spoke at the same industry conference.

Brennan noted that the countries' borders remain in place, but the governments have lost control of them to IS.

In the last month, Turkey also has regularly crossed its border with Iraq to stage air strikes against Kurdish rebels in Iraq territory, and this week Turkey staged its first ground invasion of Iraqi Kurdistan since 2011.

The incursion drew only a weak response from Baghdad, which on September 10 protested the "clear violation of Iraqi sovereignty."

Not only have the borders become blurred, Brennan said, but Iraqis and Syrians now more often identify themselves by tribe or religious sect, rather than by their nationality.

"I think the Middle East is going to be seeing change over the coming decade or two that is going to make it look unlike it did" in the past, Brennan said.

Iraq and Syria were artificial creations of British and French diplomats when the Ottoman Empire disintegrated on the eve of World War I. Each contains communities of Sunnis, Shi'a, and Kurds.

Iraq is run by a Shi'ite-dominated government with ties to Iran, while the Bashar al-Assad government in Syria is dominated by Alawites, also a Shi'ite sect. They are each fighting IS.

The Obama administration's official policy is that Iraq and Syria remain internationally recognized nation-states.

Administration officials, for example, have resisted calls to send arms directly to the Kurds, who have been the United States' most loyal ally in the fight against IS. The administration has insisted that arms for the Kurds be routed through the government in Baghdad.

But in 2006, then-Senator Joe Biden argued for splitting Iraq into three autonomous ethnic zones with a limited role for a central government. The George W. Bush administration sought to keep Iraq unified at that time.

But eventually, Sunnis became disaffected with a Shi'ite government in Baghdad that excluded them. Kurds have been in constant disputes over budgets and oil with Bagdad, and they have seized control of the strategic northern oil city of Kirkuk.

In Syria, the Assad government is hanging on with increasing support from Russia, leaving the country divided among government, rebel-held, and IS territory.

With reporting by AP, AFP, Foreign Policy, and CNN