Bahman Golbarnezhad's death after falling from his bike during a race is probably the first in the games.
Iranian cyclist Sarafraz Bahman Golbarnezhad has died after crashing in a road race at the Paralympics on Saturday.
The International Paralympics Committee said Golbarnezhad, 48, fell from his bike at a mountainous stretch during a racing event. He received emergency treatment at the roadside and was taken to hospital where he later died.
The IPC said he suffered cardiac arrest on the way to the hospital.
"With immense regret we have to say Sarafraz Bahman Golbarnezhad...has died after an accident while racing," Iran's Paralympic Committee said in a statement.
The IPC said it believes this is the first death in a Paralympics.
The cause of the crash was not clear, and officials said it was being investigated.
"The Paralympic family is united in grief at this horrendous tragedy, which casts a shadow over what have been great Paralympic Games," IPC President Philip Craven said.
The Iranian flag was lowered to half-staff in the Paralympic Village, and at the venue where Iran faces Bosnia and Herzegovina in a men's sitting volleyball final on Sunday.
A moment of silence will also be held at Sunday's closing ceremony in Maracana Stadium.
"This is very sad news for sport and for the Paralympic movement." Carlos Nuzman, head of the Rio Olympic organizing committee, said in a statement. "Our hearts and prayers are with Bahman's family, his teammates and all the people of Iran."
Moment when Iranian para-cyclist Bahman Golbarnezhad dies in crash - Rio... Rip Golbarnezhad https://t.co/4KGQG49bxv— michael (@michaellv93) September 17, 2016
A Paralympic biography said Golbarnezhad was born in Shiraz, Iran. He also competed in the London Paralympics but didn't win any medal. He was competing in the C4-5 races for athletes with lower limb impairments or amputations.
This was his second race in Rio. On Wednesday, he finished 14th in a time trial.
Golbarnezhad was an experienced Paralympian competing on a route that included the Gruman circuit used in last month's Olympic road races.
"He was an exemplary Paralympic sportsman who, with love and energy, tried his best to promote the name of Iran and to make all of us proud and at the end he gave his life for this," said Iran's Paralympic Committee.
"All members of the Iranian cultural and sports camp here express condolences to his family and the Iranian nation. The name of Bahman Golbarnezhad will be inscribed in the proud history of Iranian Paralympics."