Nigeria's army chief, Lieutenant General Ibrahim Attahiru, died in an air force plane crash on Friday.
He was on an official visit to the northern state of Kaduna, which has had security challenges in recent months.
The air force said in a statement that its plane crashed near Kaduna airport and that it was investigating the cause.
The presidency added that other military officers were also killed in the crash.
President Muhammadu Buhari, in a presidency statement, described the crash as a "mortal blow ... at a time our armed forces are poised to end the security challenges facing the country."
Nigeria, Africa's most populous nation, has had poor air safety record in the past, although it has improved in recent years.
Buhari appointed Attahiru alongside other military chiefs in January after years of mounting criticism over spreading violence by insurgents and armed gangs.
Hamas handed over three Israeli hostages on Saturday, whose emaciated appearance shocked Israelis following their release on live TV, in the latest stage of a ceasefire deal aimed at ending the 15-month war in Gaza.
The US Coast Guard in Alaska found the wreckage of a small plane atop frozen sea ice on Friday, after the aircraft suddenly lost altitude on Thursday and the crash killed all 10 people on board, officials said.
A US judge has temporarily allowed roughly 2,700 US Agency for International Development employees put on leave by President Donald Trump's administration to go back to work, pausing aspects of a plan to dismantle the agency.
Hamas accused Israel of multiple breaches of their ceasefire agreement on Friday, a day before the scheduled exchange of three more Israeli hostages for Palestinian prisoners in the latest stage in a fragile deal aimed at ending the war in Gaza.
His Highness Sheikh Mohammed bin Rashid Al Maktoum, Vice President and Prime Minister of the UAE and the Ruler of Dubai will meet with a group of young humanitarians at a ceremony on February 23, as part of the Arab Hope Makers initiative.
The UAE Floating Hospital in Al-Arish has admitted around 30 patients from Gaza since the start of the ceasefire and the resumption of medical evacuations through the Rafah crossing, as part of the Operation Chivalrous Knight 3.
The UAE on Friday strongly condemned a shooting at an adult education centre in Sweden that killed 11 people, expressing solidarity with the victims' families.