An explosion has killed several people at a large rally by supporters of Ethiopia’s new, reformist Prime Minister Abiy Ahmed in the capital, Addis Ababa.

In a televised address shortly after Saturday’s blast, Abiy said “a few people” were killed in the what he called a “well-orchestrated attack”, offering his condolences to families of the victims.

Fitsum Arega, the prime minister’s chief of staff, said on Twitter that unidentified assailants launched a grenade attack at the rally.

“Some whose heart is filled with hate attempted a grenade attack. HE PM Abiy is safe. All the casualties are martyrs of love & peace. HE PM sends his condolences to the victims. The perpetrators will be brought to justice,” Arega said.

In addition to those killed, at least 20 people were admitted to hospital with serious injuries from the blast, a local journalist told Al Jazeera.

Footage of the rally showed Abiy being rushed from the scene by security guards.

Update: A footage from Ethiopian News agency shows PM #AbiyAhmed whisked away by his security detail. A faint sound of explosion can be heard over the MC who was thanking those Ethiopians watching the program from abroad. The crowd is dispersing and no further alert as of now. pic.twitter.com/Ls0n6oPWIs

— Addis Standard (@addisstandard) June 23, 2018

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

Ambulances were at the scene in the crowded Meskel Square in Addis Ababa where the prime minister had been addressing thousands of supporters.

In a hat and T-shirt, Abiy addressed the crowd as supporters wore clothes displaying his image and carry signs saying “One Love, One Ethiopia”.

The explosion occurred shortly after Abiy finished speaking and was waving to the crowd.

#Ethiopia Breaking News – Still ongoing event at Meskel Square. Ambulance is on fire! This is right after PM Speech! pic.twitter.com/ktXz988wD4

— Ethiopia RISE! (@EthiopiaRise) June 23, 2018

Ethiopians had packed the square in a show of support for Abiy’s reformist agenda, with numbers unseen in recent years in the East African nation.

As part of the promised reforms, Abiy has 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.