Guard fatally stabbed outside Brazil embassy in Tunisia
The guard "was wounded by a sharp object" wielded "by a person he was questioning over the reason for his presence in the perimeter of the embassy", the ministry said in a statement.
He died at a hospital shortly after, interior ministry spokesman Faker Bouzghaya told AFP.
"This is a criminal act unrelated to terrorism," by a suspect who was "mentally troubled", he added.
Security forces fired at the suspect, wounding him in the leg, before taking him into custody, according to the ministry.
Authorities have not identified the man, who was transported to hospital for treatment.
The North African country suffered a string of deadly jihadist attacks after its 2011 revolt which toppled dictator Zine El Abidine Ben Ali and sparked the Arab Spring uprisings across the region.
Tunisian authorities say they have made significant progress in the fight against violent extremist groups in recent years.
However, a deadly mass shooting hit the Tunisian resort island of Djerba last month.
The gunman, a police officer, killed three other officers and two Jewish worshippers, most of them outside a synagogue, before being shot dead himself by police.