Tunisian opposition politician Chokri Belaid has been shot dead outside his home in the capital, Tunis, his brother and officials say.
They say that Chokri Belaid was shot in the neck and head on his way to work.
Mr Belaid was the co-ordinator of the left-leaning Democratic Patriots party.
Tunisia is gripped by a political crisis as talks on a long-awaited cabinet reshuffle to include a wider range of parties in a coalition led by by the Ennahda party have broken down.
“My brother was assassinated. I am desperate and depressed,” Mr Belaid’s brother Abdelmajid Belaid told the AFP news agency.
It is not known who is responsible for the attack on the politician.
On Saturday he accused “mercenaries” hired by the Ennahda party of carrying out an attack on a Democratic Patriots meeting.