Hachalu Hundessa, famed for his political songs, came to be seen as a voice for the Oromo people during years of anti-government protest that swept Abiy to power in 2018.
At least three people have been killed and others critically injured when protests erupted in Ethiopia after a prominent singer from the country's largest ethnic group was shot dead.
Youths enraged by the killing of a popular protest singer burned tyres during demonstrations on Tuesday in Ethiopia's capital, in a display of anger from the prime minister's own Oromo ethnic community.
There was also heavy violence in the town of Adama, with victims reporting they had been shot by security forces, said Dr. Desalegn Fekadu, a surgeon at the Adama Hospital.
"There are a lot of casualties, most of them are bullet injuries. Three patients died and there are still critical patients," he told AFP.
"There are also more than 10 patients with burn injuries. They said their houses were set on fire."
Spokesmen for the federal police and the Oromia regional police said they did not have any immediate information on casualties.
Addis Ababa city police commissioner Getu Argaw told state media late on Monday that Hachalu Hundeessaa had been shot dead at around 9:30 in the evening. Some suspects had been detained, he said, giving no further details.
On Tuesday morning the normally busy streets of Addis Ababa were eerily empty as protesters lit fires and chanted slogans.
The internet connection to Ethiopia, Africa's second most populous nation, appeared to be down, a common occurrence during political protests.
Prime Minister Abiy Ahmed expressed his condolences, promised an investigation and asked the public to remain calm, in a message posted on Twitter.
Haacaaluu, a former political prisoner, rose to prominence during prolonged anti-government protests which propelled Abiy into office in 2018.
Abiy's Oromo ethnic group sparked the protests, and his rise to power ended decades during which the multi-ethnic ruling coalition was dominated by ethnic Tigray leaders.
His rule has ushered in greater political and economic freedoms in what had long been one of the continent's most repressive states, and he won the 2019 Nobel Peace Prize for ending conflict with neighbouring Eritrea.
But the rise in political activism has also led to an increase in unrest in a country made up of more than 80 ethnic groups. Abiy's rule has been frequently challenged by local powerbrokers demanding more access to land, power and resources.
His pan-Ethiopian politics have sparked a backlash from some elements of his own Oromo powerbase, spearheaded by a media magnate, Jawar Mohammed.
"They did not just kill Hachalu. They shot at the heart of the Oromo Nation, once again !!...You can kill us, all of us, you can never ever stop us!! NEVER !!" Jawar posted on his Facebook page on Tuesday.
Clashes between police and Jawar's supporters killed at least 78 people in October last year after the government tried to withdraw Jawar's security detail.
Elections due this year have been postponed until next year due to Covid-19 in a deal agreed with the major opposition parties.