More than 150 people were also injured in the blast, which appeared to target Abiy Ahmed just as he was wrapping up a speech to a cheering crowd of hundreds of thousands in the heart of Addis Ababa.
“The US government said it will send FBI experts to investigate Saturday’s bomb blast,” State-affiliated Fana Broadcast Corporate reported, without giving further details.
A spokesman for the US embassy in Addis Ababa confirmed the FBI’s involvement.
An AFP photographer on Monday saw four people who did not appear to be Ethiopian combing the site of the blast while a US embassy vehicle was parked nearby.
Ethiopian security forces have arrested 30 people suspected of involvement in the blast, though no party has claimed responsibility.
Nine police officers have also been detained for failing to prevent the attack, including the capital’s deputy police commissioner.
Rally organiser Seyoum Teshome earlier told AFP he saw police scuffle with a person attempting to hurl a grenade at the stage Abiy had spoken from.
It then detonated in the crowd, sparking panic and a stampede that injured scores.
The attack was a rare act of violence in the heavily policed capital but does not appear to have derailed the reform agenda of Abiy, who took office in April.
– Reforms unshaken –
On Monday, Fana reported that a delegation from neighbouring Eritrea was due in Addis Ababa this week, in what would be a rare diplomatic meeting between the long hostile neighbours.
Eritrea and Ethiopia have been at loggerheads for years over Addis Ababa’s refusal to withdraw from territory a United Nations-backed boundary commission says belongs to Eritrea.
Earlier this month Abiy reversed that policy, saying Ethiopia would respect the demarcation handed down after a 1998-2000 war between the two countries that killed an estimated 80,000 people.
In the past it would not have been surprising for Eritrea to be blamed for an attack such as Saturday’s. Both countries have hosted rebel groups bent on overthrowing the others’ government but Abiy’s moves have calmed tensions.
Last week the Ginbot 7 radical opposition group said it would stop attacks on Ethiopia to support Abiy’s reforms, and later even issued a statement condemning the Meskel Square attack.
The Eritrea rapprochement is one of several changes Abiy has made since the ruling Ethiopia People’s Revolutionary Democratic Front (EPRDF) selected him to take over following his predecessor’s surprise resignation.
Abiy has since released jailed journalists and dissidents, admitted that security forces tortured people and begun to open up the state-controlled economy.
These moves have boosted his popularity among Ethiopians.
The 42-year-old former army officer and cabinet minister is the first prime minister in modern Ethiopia from the country’s largest ethnic group the Oromo.
The Oromos along with the second-largest the Amharas staged months of anti-government protests starting in late 2015 that prompted the government to declare a 10-month state of emergency in October 2016.
The unrest along with disagreements within the EPRDF over how to deal with it prompted Hailemariam Desalegn to resign the prime minister’s post last February.
A secretive coalition of four ethnically based parties, the EPRDF controls every seat in parliament and wields unchecked control of Ethiopia’s institutions. Abiy’s level of support within the party leadership remains unclear.