Voters Monday in Kirkuk, Iraq. (Chris McGrath/Getty Images)

Kurds packed polling stations across northern Iraq on Monday in a historic referendum on independence despite vigorous opposition from the country's central government as well as regional and world powers.

Church bells tolled, and imams implored Kurds over mosque loudspeakers to vote when polls opened across the Kurdish region — a swath of mountains, oil fields and desert that has been run as a semiautonomous enclave for decades.

The poll is expected to produce an overwhelming “yes” result that many Kurds see as the culmination of a century-long and bloody struggle for self-determination. Kurdish authorities said that 3.9 million people were eligible to vote and that final results were expected by Thursday.

As polls closed at 7 p.m., Iraq’s defense ministry said it had started joint military exercises with the Turkish army along the shared border near Kurdish territory, heightening fears that the vote could set off another unpredictable and destabilizing cascade across the region.

Iran also launched military exercises along its borders with the Iraqi Kurdistan region ahead of the vote.

Turkey and Iran worry that Kurdish secession in Iraq could further embolden their own Kurdish minorities, including a separatist faction that has fought Turkish forces since the 1980s.

The United States, traditionally a strong ally of Iraq's Kurds, has said the timing of the referendum threatens the fight against the Islamic State. U.S. officials also worry that the Kurdish move will weaken Iraqi Prime Minister Haider al-Abadi ahead of national elections next year while empowering sectarian political forces.

On Monday, State Department spokeswoman Heather Nauert said the United States is "deeply disappointed" that the Kurdistan regional government decided to conduct the referendum but added that Washington's "historic relationship with the people of the Iraqi Kurdistan Region will not change" in light of it.

For his part, Abadi tried up to the last minute to block the vote, and Iraqi leaders say they will not recognize the outcome — setting up a potential political standoff.

The United States, Iran and Turkey have called the referendum illegitimate and have also vowed not to recognize its results, saying it is a dangerous step toward the division of the country.

But Iraqi Kurds appeared intent on sending a powerful message as a distinct political force with a culture, language and history of their own. Many voters perceived the referendum as a symbol of their unity and separate political path rather than an immediate separation from Iraq.

Members of a Kurdish peshmerga battalion show their ink-stained fingers after casting their vote Monday in Irbil, Iraq. (Safin Hamed/AFP/Getty Images)

On Sunday, the Kurdish regional president, Masoud Barzani, whose party and powerful political family have been the primary engine behind the independence push, said the vote is the beginning of a years-long separation process from Iraq that he hopes will be achieved through dialogue and negotiations.

Lamia Amin, 60, linked arms with her blind husband as they walked out of a polling place in a working-class section of Irbil, the Kurdish regional capital. She said she could not sleep the night before, out of excitement about the referendum.

Amin, the mother of a police officer and a member of the Kurdish fighting force known as the peshmerga, said she cast her vote in honor of her brother, who was killed fighting in an insurrection against then-dictator Saddam Hussein in 1991 in the aftermath of the Persian Gulf War.

She eagerly showed that she had changed her Facebook profile photo to a picture of her brother.

“God willing, we will have a country,” she said. “We have sacrificed so much, waited so long. We can wait a little longer.”

Her husband, Mohammed Sharif, 72, smiled and said Kurds will be remembered as “Hollywood heroes” for their determination.

Polling places also drew members of minority groups in the Kurdish region, such as Sunni Arabs. But many people who were technically ineligible to cast ballots, such as Arab refugees in Iraqi Kurdistan and Kurds who live in Baghdad, said they were permitted to vote anyway.

Khalil Hassan, 70, angrily railed against the central government of Iraq, which he accused of displacing him from his home in Salahuddin province in 2015 with its airstrikes during a campaign to uproot Islamic State militants. Since then, he said, he has lived in Kurdish territory as an internally displaced person.

"I voted for Kurdistan because the Shiites, the Iraqi government, destroyed our homes and had no mercy for anyone," he said. "No one has ever insulted me here. We support Masoud Barzani with our voices and our blood."

International observers expressed concerns that individual results will not be released by region or district, making it impossible to know how people in disputed areas voted.

Iraq and the United States were especially troubled by the Kurdish decision to include ethnically mixed cities, such as oil-rich Kirkuk, that have been historically claimed by both Kurds and Arabs.

In a sign of the regional spillover from the vote, Turkish President Recep Tayyip Erdogan on Monday threatened tough action against the Kurdish authorities, including the cutting off of a pipeline carrying oil from northern Iraq across the Turkish border, as well as unspecified military action and other measures.

Turkey, which has battled a decades-long insurgency by Kurdish militants at home, has become alarmed of late by increasingly assertive movements for Kurdish independence across its borders in Syria and Iraq. Erdogan has also faced pressure from Turkish nationalists who vehemently oppose Kurdish autonomy.

On Monday, Turkey’s strident opposition to the ballot was splashed across the front pages of the country’s newspapers.

Barzani, the Kurdish regional president and an erstwhile ally of the Turkish government, was referred to as “insolent” and the vote as “chaos.”

“You’re itching for it, Barzani,” one headline said, splashed above photos of tanks rolling across the desert.

Erdogan warned that Turkey could block Iraqi Kurdistan's oil exports. "Turkey is in control of the tap," he said during an appearance in Istanbul on Monday, referring to a pipeline that carries hundreds of thousands of barrels of oil from northern Iraq across Turkey to the Mediterranean Sea.

Iran on Sunday closed its airspace to flights to and from Iraqi Kurdish cities administered by the Kurdistan government in Iraq, while Iraq's central government demanded that all ports and oil terminals in the Kurdish-controlled areas be handed back to federal custody.

U.S. officials have privately expressed frustration, viewing the referendum as a vehicle to keep Barzani in power. Barzani’s term as regional president expired in 2015, but he has refused to step down — although he has indicated he will not run in elections scheduled for November.

The referendum was not initially backed by all Kurdish parties, but as international opposition grew, internal disputes over its timing were settled, and the vast majority of the Kurdish political class has come out in support of the vote.

Bashar Warda, the archbishop of the Chaldean Catholic Church in Irbil, said he hoped that the bellicose language between the two sides would subside and that Baghdad would recognize the peaceful democratic exercise and move forward with dialogue.

"Voting is such a peaceful event," Warda said as he left a polling place in the Christian enclave of Ankawa with members of his congregation. "In the Middle East, usually when a group wants to gain something, it is through violence. As a church, we will support a peaceful, mutual dialogue."

Fahim reported from Istanbul. Brian Murphy in Washington contributed to this report.

Read more