The four ethnically based parties in the coalition that has ruled Ethiopia since 1991 are facing increasing competition from new, more strident parties demanding greater power and resources for their own regions.
"For a prime minister whose popular legitimacy relies on his openness, recent protests in Oromiya could be politically suicidal," said Mehari Taddele Maru, an Addis Ababa-based political analyst. "It signals a significant loss of a populist power base that propelled him to power."
If next year's elections are fair - as Abiy has promised they will be - they will test whether the young prime minister can hold together his fractious nation of 100 million people and continue to open up its state-owned economy, or whether decades of state repression have driven Ethiopians into the arms of the political competition.
Jawar said he hadn't decided who else he would support in next year's polls, or whether he would run himself. His Twitter feed has been teasing the possibility last weekend: "The story about me running for office is just speculation. I am running to lose weight."
He refused to be drawn on Friday, telling Reuters: "I don't exclude anything."
His remarks were his strongest criticism yet of Abiy, with whom he was photographed frequently last year, but the split follows pointed remarks by Abiy to parliament on Tuesday.
Abiy said, without naming anyone, "Media owners who don't have Ethiopian passports are playing both ways ... If this is going to undermine the peace and existence of Ethiopia ... we will take measures."
The comments were widely seen as a dig at Jawar, who is Ethiopian-born but has a U.S. passport and returned from exile last year.
Abiy didn't create Ethiopia's ethnic divisions, but he must address them, said Abel Wabella, a former political prisoner who is now editor of the Amharic-language newspaper Addis Zeybe.
Jawar is "testing the waters," he said. "Ethnic federalism creates monsters ... if Abiy fails to dismantle the power groups based on ethnicity, and to address the structural problems we have as a nation, we will end up in civil war."
