ADDIS ABABA, Ethiopia -- An explosion struck a huge rally for Ethiopia's reformist new prime minister on Saturday shortly after he spoke and was waving to the cheering crowd that turned out to support sweeping changes in Africa's second most populous nation.

Addressing the country minutes after he was rushed to safety, Prime Minister Abiy Ahmed called the blast a "well-orchestrated attack" but one that failed. He did not lay blame but said police were investigating. Health Minister Amir Aman confirmed one death while Abiy's chief of staff said 83 people were hurt, six critically.

"The prime minster was the target," a rally organizer, Seyoum Teshome, told The Associated Press. "An individual tried to hurl the grenade toward a stage where the prime minister was sitting but was held back by the crowd."

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The man with the grenade was wearing a police uniform, witness Abraham Tilahun told the AP. Police officers nearby quickly restrained him, he said. "Then we heard the explosion."

AP video from the scene showed bloodstained ground and abandoned shoes while people chanting the prime minister's name fled, some clutching their heads in shock and despair.

The attack was "cheap and unacceptable," Ethiopia's prime minister said, and added: "Love always wins. Killing others is a defeat. To those who tried to divide us, I want to tell you that you have not succeeded."

The explosion in packed Meskel Square in the capital, Addis Ababa, came after weeks of reforms that had shocked many in the East African nation after years of anti-government tensions, states of emergency, thousands of arrests and long internet shutdowns.

The 42-year-old Abiy took office in April and quickly announced the release of tens of thousands of prisoners, the opening of state-owned companies to private investment and the unconditional embrace of a peace deal with rival Eritrea. Websites were unblocked and opposition figures were invited to dinner. Ethiopians said they could hardly keep up with the pace of change.

Saturday's rally began as a show of exuberance, with supporters wearing clothes displaying Abiy's image and carrying signs saying "One Love, One Ethiopia."

Informal in a neon green T-shirt, Abiy told the tens of thousands of supporters that change was coming and there was no turning back.

"For the past 100 years hate has done a great deal of damage to us," he said, stressing the need for even more reforms.

After the explosion the state broadcaster quickly cut away from coverage of the rally, which broke up with people singing, chanting and going back to their homes.

"I've never thought this day will come in Ethiopia. I'm very emotional right now," said Mulugeta Sema, a supporter of Abiy who wore a T-shirt with the new leader's image and spoke before the blast. "We should never get back to dictatorship. This is time for change."

In a notable sign of the new effort at dialogue between bitter rivals after a deadly border war and years of skirmishes, one diplomat for Eritrea, ambassador to Japan Estifanos Afeworki, said on Twitter that his country "strongly condemns the attempt to incite violence" in Saturday's attack.

The United States has been among those in the international community expressing support for the dramatic changes in Ethiopia, a key security ally in a turbulent region with neighbors including Somalia and South Sudan.

Not everyone has cheered the reforms. Some Ethiopians in the north near the border with Eritrea, one of the world's most reclusive nations, have protested the embrace of the peace deal. And the Tigrayan People's Liberation Front, a party in Ethiopia's ruling coalition that has been the dominant force in government for most of the past 27 years, said the announcement on the peace deal had been made before the ruling coalition's congress met to discuss it: "We see this as a flaw."

Abiy is the first prime minister from the Oromo ethnic group, the largest in the country, since the ruling party came to power in 1991. Ethiopia's sometimes deadly protests demanding more freedoms began in the Oromia and Amhara regions in late 2015 and spread elsewhere, finally leading to the resignation of Prime Minister Hailemariam Desalegn early this year.

Abiy visited the restive regions shortly after taking office and stressed the importance of resolving differences through dialogue instead.