An official in Argentina's Senate says a legislator has died three days after being seriously wounded in a gun attack that killed a provincial official.

Acting Senate president Federico Pinedo said Sunday that Chamber of Deputies member Héctor Olivares died of his wounds.

At least six people have been detained in what has been described as a "mafia-style" attack Thursday that shocked Argentines. Officials have said two gunmen in a parked car shot wounded Olivares and killed Miguel Marcelo Yadón near the country's congressional building in Buenos Aires.

Olivares was a representative from La Rioja province in the lower house of congress. Yadón worked for La Rioja's federal electric transportation system.

Authorities have said investigators are still trying to determine a motive.