LAGOS (Reuters) - Amnesty International accused Nigerian security forces on Thursday of killing at least 150 peaceful advocates of Biafra’s secession from Africa’s most populous nation, but the military and police dismissed the allegations.

An army spokesman said Amnesty’s statement, the latest in a series of allegations of impropriety levelled against Nigeria’s military in the last year, aimed to tarnish the security forces’ reputation. The police said they did not attack people holding demonstrations.

Amnesty said the military fired live ammunition, with little or no warning, to disperse members of the Indigenous People of Biafra (IPOB) group between August 2015 and August 2016.

Its 60-page report based on interviews with 193 people, 87 videos and 122 photographs from that period also said troops and the police used “arbitrary, abusive and excessive force to disrupt gatherings”.

Secessionist feeling has simmered in the southeast since the Biafra separatist rebellion tipped the west African country into a 1967-1970 civil war that killed an estimated 1 million people.

It flared up again last year after IPOB leader Nnamdi Kanu was detained on charges of criminal conspiracy and belonging to an illegal society. That prompted supporters of Kanu to hold protests that Amnesty said were dispersed with live ammunition.

Army spokesman Sani Usman said Biafra separatists had behaved violently, killing five policeman at a protest in May and attacking both military and police vehicles.

“The military and other security agencies exercised maximum restraints despite the flurry of provocative and unjustifiable violence,” said Usman.

Nigeria Police Force spokesman Don Awunah said officers “always abide by the law” and adhere to best practices. “We don’t attack people who are demonstrating, which every Nigerian has a right to do,” he said.

Witnesses told Amnesty that some protesters had thrown stones, burned tyres and, in one incident, shot at the police but added that “these acts of violence did not justify the level of force used against the whole assembly”.

“This reckless and trigger-happy approach to crowd control has caused at least 150 deaths,” said Makmid Kamara, interim director of Amnesty International Nigeria, who called on authorities to launch an investigation into the matter.

He said the government’s deployment of troops at the events seemed “in large part to blame for this excessive bloodshed”.

The report is the latest in a string of accusations levelled at the army by Amnesty. Last year it said more than 8,000 people died in detention during a crackdown on Boko Haram.

It also said soldiers killed hundreds of Shi’ite Muslims in the northern city of Zaria in December 2015. A judicial inquiry in August concluded that 347 people were killed and buried in mass graves after those clashes.