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.
President Donald Trump capped the first day of his Republican Party's first-ever midterm convention by proposing to pay every US adult a $5,000 "Trump dividend" if his party wins November's congressional elections.
A large-scale search and rescue operation was underway off the western Philippine island of Palawan on Thursday after a passenger ferry caught fire, killing five people and leaving dozens of passengers missing.
President Donald Trump said he expected the war with Iran to end after the November US midterm elections after the two sides launched their biggest wave of attacks on shipping since the start of the six-month-old war.
At least 20 people have been killed in a fire aboard a foreign cargo vessel undergoing repairs at a state-owned shipyard in the eastern Chinese city of Qingdao on Thursday, state media reported, with five others still missing.
The US military said on Wednesday three people have been killed in a strike on a vessel in the Caribbean Sea, the latest in a series of attacks that Washington says target "narco-terrorists" but human rights groups condemn as extrajudicial killings.
At least 14 people were killed and 11 wounded on Wednesday in an explosion at a temporary site used to store weapons and remnants of war near the Syrian city of Sarmada in Idlib province, state television reported.
The United States has destroyed five Iranian oil carriers on Tuesday after the Islamic Revolutionary Guard Corps (IRGC) targeted its navy warship with ballistic missiles "twice over the past two days".
Britain's NATS air traffic control provider has a week to investigate the systems failure that halted flights and stranded hundreds of thousands of passengers, the government said, as pressure mounts on its chief executive.
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Trump touts $5,000 payout if Republicans win as Vance waits in wings
Search expands after Philippine ferry fire kills five and leaves dozens missing
Trump says Iran war to end after US midterm elections
At least 20 killed in cargo vessel fire at China shipyard, state media reports
US military says it struck vessel in Caribbean, killing 3
At least 14 killed in explosion at weapons depot in Syria
US hits five Iranian oil tankers after attack on Navy ships
UK gives air traffic provider a week to probe outage that halted flights
