Bulgaria's President Rosen Plevneliev is due to renew his attempts at triggering a national poll on election rules in June this year, his Chief of Staff Ekaterina Zaharieva has said.

Zaharieva, who was also Deputy PM in last year's interim government, explained in an interview for the Bulgarian National Radio that the President still believes "people's demands have to be heard".

Her words follow last week's address of Plevneliev in Parliament, when the head of state reiterated he would still seek to trigger a referendum on voting rules.

In 2014 he divided public opinion when he said Bulgarians should have a say on three issues, including the introduction of majority elections, compulsory voting, and electronic voting.

But Parliament refused to give the green light to a petition signed by more than 500 000 people that called for the referendum, adding a vast part of the signatures were void.

Last week Plevneliev did not specify whether the options put forward in the referendum would include the same issues this year.