Bulgaria's long-time Prime Minister Boyko Borisov said Wednesday that he would not seek a new mandate as premier after this month's election resulted in a fragmented parliament.

Borisov's centre-right GERB party came first in the election, but the three-time premier admitted last week that he would not have the backing to ensure that a new government is accepted by parliament.

Nonetheless, he said he will propose a new cabinet even if it stands a slim chance of approval -- but without him at the helm.

-I won't be a candidate for the post of prime minister- the 61-year-old, who has ruled the EU member state virtually uninterrupted for a decade, declared on social media.

He said he did not want to "divide the nation".

-I will put forward another PM designate with a clear European and NATO orientation- he added, although he did not say who he would propose.

Huge anti-corruption protests shook Borisov's government last year, with demonstrators accusing it of favouritism, dependence on powerful oligarchs and weaponising prosecutions against political opponents.

After winning less than 27 percent of the vote in the April 4 election, GERB has just 75 lawmakers in the 240-seat parliament and lacks partners to govern.

If GERB's cabinet fails to secure parliamentary approval, President Rumen Radev will hand the mandate to form a government to the surprise second-placed anti-establishment party There is Such a Nation (TSN).

TSN leader Slavi Trifonov, a showman and TV presenter, is in isolation after contracting the coronavirus and has not yet spoken about his plans.

If TSN also fails to form a cabinet or win parliamentary approval, the mandate will go to a third and last party of Radev's choice.

If that party also fails, fresh elections will be called.