Ethiopians voted on Monday in national and regional elections as long lines of voters were seen in some parts of the capital, Addis Ababa, while security was stepped up across Africa's second most populous country.

Military vehicles were parked in key locations in the capital. More than 37 million Ethiopians were expected to vote. 

Ethiopia had previously slated June 5 as a tentative schedule to hold the country's sixth general elections. However, delays in nominating and training electoral staff as well as delays in printing and distributing ballots forced a postponement.

"Insecurity, malfeasance, and logistical challenges witnessed in parts of the country mean that voting in those affected areas will take place at a later date. And due to the violent conflict and crisis in Tigray, citizens in that region will not go to polls on June 21 either," said Birtukan Mideksa, chairperson of the National Electoral Board of Ethiopia (NEBE). 

Monday's vote involves more than 40 parties and 9,500 candidates, according to AFP citing the NEBE, adding that the electoral board says it is ready for the crucial vote and is certain it will be credible.

Under Ethiopia's parliamentary government system, the prime minister, who is the highest authority in the country, is selected from the party that wins the most seats at the federal parliament level, and will be sworn in after the parliamentary vote.

On Monday, United Nations Secretary-General Antonio Guterres urged Ethiopian authorities, political leaders and their supporters to ensure that all voters are able to cast their ballots freely and peacefully.

Through a statement delivered by his spokesperson Stephane Dujarric, the UN chief noted that the elections are taking place "in a challenging political and security environment" and called on all stakeholders "to refrain from any acts of violence or incitement."

"The secretary-general encourages leaders and participants in the elections to promote social cohesion and reject hate speech. He stresses that any electoral disputes should be resolved through dialogue and established legal channels," the statement read. 

(With input from agencies)