ADDIS ABABA, Ethiopia — A thwarted attempt to hurl a grenade at Ethiopia's reformist new prime minister led to a deadly explosion Saturday at a massive rally in support of sweeping changes in Africa's second most populous country. Nine police officials were arrested, state media reported.

Witnesses said a man tried to throw the grenade at the stage as Prime Minister Abiy Ahmed waved to the cheering crowd of tens of thousands shortly after he made a strong appeal for unity following months of anti-government protests.

Addressing the nation minutes after he was rushed to safety, Abiy called the blast a "well-orchestrated attack" but one that failed. He did not lay blame and said police were investigating. At least one person was killed and 155 people were hurt, nine critically, Health Minister Amir Aman said.

"The prime minister 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."

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."

Nine police officials were arrested, including the deputy head of the capital's police commission, state broadcaster ETV reported.

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.

An injured man is helped by others as security officers gather at the scene of an explosion during a massive rally to support the country's new reformist prime minister Abiy Ahmed in Meskel Square in Addis Ababa, Ethiopia on June 23, 2018. Stringer / EPA

The attack was "cheap and unacceptable," the 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 ruling party in a statement blamed "desperate anti-peace elements" and vowed to continue with the country's reforms.

The explosion in packed Meskel Square in Addis Ababa followed weeks of dramatic changes that 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."