The deputy commissioner of the Addis Ababa Police Commission has been arrested over shortcomings in security after a grenade attack in the Ethiopian capital killed one person and left more than 100 wounded, according to state-run TV.

"Nine individuals, including the Deputy Commissioner of the Addis Ababa Police Commission, are in custody and under investigation over shortcomings" in security, the Ethiopian Broadcasting Corporation said

The attack was launched by an unidentified assailant moments after the 41-year-old prime minister, a former soldier who took office in April, finished his speech to tens of thousands of people gathered in the centre of Addis Ababa.

A witness saw Mr Abiy whisked away by guards. Another witness told Reuters the assailant with the grenade had been wrestled to the ground by police before it exploded.

Health Minister Amir Aman said one person was killed and 154 were wounded, with 10 of them in critical condition.

Addressing the nation on television shortly after the blast Mr Abiy said the attack was an "attempt by forces who do not want to see Ethiopia united."

Mr Abiy had promised the crowd in his speech in Addis Ababa's Meskel Square that he would bring more transparency to government and reconciliation to a nation of 100 million people that has been torn by protests since 2015.

Eritrea, which has long been at loggerheads with Ethiopia over a border row that Mr Abiy has sought to resolve, condemned the incident, as did the European Union and the United States.

Mr Abiy took office after his predecessor, Hailemariam Desalegn, resigned in February following protests in which hundreds of people were killed between 2015 and 2017.

Emergency law was temporarily imposed to quell the unrest and was lifted this month.

Despite boasting one of Africa's fastest growing economies, opponents say the benefits have not been shared fairly between ethnic groups and regions in the country, which has been run by the same ruling coalition for more than 25 years.

Mr Abiy has travelled around the nation, promising to address grievances as well as political and civil rights.

After the blast, the prime minister's chief of staff wrote on Twitter: "Some whose heart is filled with hate attempted a grenade attack."

"All the casualties are martyrs of love and peace. The perpetrators will be brought to justice," Fitsum Arega wrote.

The US embassy in Addis Ababa said: "Violence has no place as Ethiopia pursues meaningful political and economic reforms."

Rally organiser Seyoum Teshome told Reuters he saw five people injured in the blast.

"It was a grenade. Someone tried to hurl it to the stage where the prime minister was," Seyoum said.

As well as promising economic reforms, Mr Abiy stunned Ethiopians this month by saying he was ready to fully implement a peace deal with Eritrea that was signed in 2000 after a two-year war.

For years, Ethiopia refused to implement the deal, saying it wanted more talks.

The stalemate led to a military build-up and sporadic clashes on the border between Ethiopia and Eritrea, which seceded from Ethiopia in 1991 after a long war of independence.

Explosion hits Presidential rally in Zimbabwe

Meanwhile, in Zimbabwe an explosion has rocked a stadium where President Emmerson Mnangagwa was addressing a rally.

A spokesman for Mr Mnangagwa said the head of state was unhurt and was taken to safety.

Vice president Constantino Chiwenga and his wife sustained minor injuries from the blast, a source close to Mr Mnangagwa said.

The President suggested he was the target of the attack.

"I am used to these attempts," he said. He added that an object "exploded a few inches away from me - but it is not my time".

"There has been an incident at Bulawayo (White City Stadium) where the president was addressing a rally. This is now a police issue but the president is safe at Bulawayo State House," spokesman George Charamba said.

"We are still to get information on what exactly happened as we understand that some people could have been injured as this happened in the VIP tent."