ZAMFARA STATE — United Nations High Commissioner for Human Rights Volker Turk demanded independent investigations into reports that separate air attacks by Nigerian and Chadian forces in northern Nigeria killed more than 100 civilians. He cited reports of an airstrike on a market in Zamfara state on May 10 and air raids by Chadian jets against Boko Haram positions in a marshland shared by Nigeria, Cameroon, Niger and Chad.

"I am shocked by reports that Nigerian army airstrikes on a market in Zamfara state killed at least 100 civilians on 10 May and injured many more," Turk said. He also addressed the cross-border operations conducted by Chadian forces. "I am alarmed and saddened by reports of high civilian casualties in attacks since Friday by Chadian jets against Boko Haram camps on remote islands in the vast marshland shared by Nigeria, Cameroon, Niger and Chad," he said.

Air raids reportedly killed dozens of Nigerian fishermen working on islands under Boko Haram control. Footage verified by the AFP news agency showed several fishermen with severe burns being treated at a hospital in Bosso, Niger.

"It is crucial that both Nigerian and Chadian authorities conduct prompt, thorough, independent and impartial investigations into these disturbing incidents," Turk said. "Their military operations, including against Boko Haram and the so-called 'Islamic State West Africa Province', must be conducted in full compliance with international humanitarian law and international human rights law."

According to Amnesty International, the Nigerian military and "bandit" gangs killed at least 100 civilians on Sunday during the state's conflict against armed groups. The organization said many of those killed were women and children and urged authorities to immediately investigate the attack on a crowded market in Tumfa village.

The Nigerian military rejected the accounts, saying there has been no evidence of civilian casualties in attacks in northwest Zamfara state this month and calling reports of large death tolls unverified and misleading. "No credible, substantiated evidence of civilian casualties has been established through any official assessment or independent verification," Defence Headquarters spokesman Major-General Michael Onoja said.

Onoja said the strike was conducted under international humanitarian law and targeted a confirmed high-level gathering based on intelligence sources in a village where several terrorists were neutralised.

Nigeria's military has been battling a group it refers to as "bandits" in the northwest and often describes them as "terrorists". It has also been battling an armed rebellion in the northeast for 17 years.