Analysts say the public split between the country's most powerful ethnic Oromo politicians could increase political uncertainty ahead of the May polls, and hinder Abiy's reformist agenda.

In an interview with Voice of America's Affan Oromo language service on Friday night, Defence Minister Lemma Megersa criticised the move to merge the coalition of ethno-regional parties which has ruled the country for three decades.

"I have had a different perspective from the beginning of the talks about the merger of EPRDF," said Lemma, adding that "even if that is to happen it shouldn't be done in a hurried way."

Nobel Peace Laureate Abiy's plans to transform the Ethiopian People's Revolutionary Democratic Front (EPRDF) into one party have already been rejected by the Tigrayan People's Liberation Front (TPLF) -- the once dominant party of late strongman Meles Zenawi.

The three other parties last week voted to unite and form the Prosperity Party (PP), which Abiy hopes will heal ethnic divisions that have marred his rule, while critics say it will only deepen them.

Lemma also rejected Abiy's philosophy "Medemer" (Amharic for synergy) which is aimed at uniting the country.

Lemma is a former president of Ethiopia's largest and most populous regional state, Oromia and is currently vice chairman of the regional ruling party (ODP), with a large following in the region.

Abiy, himself an Oromo, came to power in April 2018 after more than two years of anti-government protests led by Ethiopia's two largest ethnic groups, the Oromo and Amhara.

Ethiopian analyst Abel Abate said the public break between the two men will likely add to political uncertainty in the country as it prepares to hold general elections next year.

"While the process to form PP out of the ashes of EPRDF has gone a considerable distance, it's far from complete yet. This public disagreement could fatally injure plans to form PP", he said.

Meanwhile, Horn of Africa analyst Rashid Abdi wrote on Twitter that Abiy was "in deep trouble" after being ditched by his "single most important pillar of Oromo support".