Ethiopia's northern Tigray region on Wednesday went ahead with regional elections in an act of strong defiance against Prime Minister Abiy Ahmed, who called the vote illegal but said the government would not respond with force.

Ethiopia had been due to hold national and regional elections on August 29 but postponed them indefinitely because of the coronavirus pandemic. Tigray opposition politicians accuse Abiy of trying to prolong his rule.

The confrontation with Tigray is the latest headache for Abiy, who is struggling to hold together a federation that stitches Ethiopia's 80 plus ethnic groups.

Abiy likened the exercise as the construction of shanties by squatters on land that they do not own.

"Those who construct a shanty are illegal dwellers as they don't have land deeds, and they don't sleep with their eyes shut," he told the state broadcaster.

After decades of repression, Abiy ushered in democratic reforms that helped win him the Nobel Prize. But the new freedoms also fuelled long-suppressed demands for more regional autonomy, rights and resources.

Even in Tigray, the TPLF is itself facing pressure from more zealous ethnic nationalists. A new party is openly pushing independence from Ethiopia. Tigrayans dominated Ethiopian politics since guerilla fighters ousted a Marxist dictator in 1991, but their influence has waned under Abiy and last year the TPLF quit his ruling coalition.

"Everybody is willing to vote here... we want to be independent, free and have a nation for all Tigrayians," said Welday Asgedom, a tourism sector worker, as he headed to the polling station to cast his ballot.

The region's population is relatively small - around 5% of Ethiopia's 109-million people - but its history in politics means it is wealthier and more influential than many other, larger regions.

Ethiopia's upper house, which mediates constitutional disputes, ruled on Saturday that the polls for regional parliaments and other positions were unconstitutional.

In the past three years, Ethiopia has faced multiple bouts of outbreaks of large-scale ethnic violence, what the government described as an attempt at a regional coup led by rogue security forces, and increasingly insistent demands from smaller ethnic groups for their own regions.

On Monday Ethiopian security officials prevented a dozen people, including four journalists and a senior think tank analyst, from flying to Tigray to cover the vote.

Abiy has not specified how he will respond to the polls, although he has ruled out using force. Analysts say the government cut the region's federal funding, which supplies around half of its budget.