Voters are heading to the polls in a controversial independence referendum in the Kurdistan Region of Iraq.
Iraq's prime minister has warned he will take ‘necessary measures to preserve the unity of the country’.
Western countries have expressed concern that the poll could provoke fresh conflict, and distract from the fight against so-called Islamic State.
But Kurds, who have long fought for their own state, have pressed ahead. The result, however, is non-binding.
A Yes result is widely expected.
Iraq has said the referendum must be suspended, but it cannot enforce that decision on the autonomous region.
Ahead of the vote, prime minister Haider al-Abadi said the vote was unconstitutional and threatened peace, adding: ‘We will take the necessary measures to preserve the unity of the country.’
He did not make clear which measures he intended to implement.
Later, his government demanded the Kurdish region hand over control of its international border posts.
It also urged other countries not to buy oil from the Kurdistan region, but instead to deal only with the government on ‘oil and borders’. Oil is one of the Kurdistan region's main exports.
The leader of Iraqi Kurds, Massoud Barzani, says that independence is the only way to guarantee the safety of his people.
‘When have we ever had stability and security that we should be concerned about losing it?’ he told the BBC in a recent interview. ‘Those who are saying this are just looking for excuses to stop us.’
But he pledged that the referendum would not affect the fight against IS.
The autonomous region in the north is run by the Kurdistan Regional government, and it is formally recognised by Iraq's 2005 constitution.
That recognition came after decades of struggling for independence by the Kurdish population, who make up only 15-20 per cent of the country's population.
In the wake of the first Gulf War, Kurdish leaders and armed forces consolidated their territory in northern Iraq, leading to the 2005 agreement.
It is the only place where the Kurdish people have formed their own government, despite many decades of armed struggle across four countries where its 30-40 million members live.
Iran and Turkey have also expressed concern that the independence referendum could provoke separatist movements among Kurds living in their own nations.
In Turkey, the Kurdistan Workers' Party is considered a terrorist organisation, and it has been engaged in a decades-long armed struggle for an independent state. A linked group, PJAK, exists in Iran.
But Kurdish fighters known as Peshmerga have been one of the most successful fighting forces against IS in Syria and Iraq.
They are considered a US military ally, although Washington does not support the referendum - favouring a series of negotiations on the future relationship between Iraqi Kurds and Baghdad.
Israel is the only nation to have openly supported the independence bid.
The Kurdish people are a distinct ethnic group spread across Iraq, Syria, Turkey, and Iran.
Polls in the independence referendum will remain open for 12 hours, until 20:00 (17:00 GMT).
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