Czech driver Ales Loprais, the leader in the truck category of the Dakar Rally, said on Wednesday he was "terribly sorry" after his vehicle hit an Italian tourist who subsequently died.
Loprais's Praga truck struck the 69-year-old Italian man who was taking pictures behind a sand dune during Tuesday's ninth stage between Riyadh and Haradh in Saudi Arabia.
He died in the helicopter taking him to hospital, organisers Amaury Sport Organisation (AMO) said in a statement, adding it was investigating the accident.
The Czech news agency CTK said later on Wednesday Loprais had quit the race.
"I would like to express my condolences to his family and friends. I'm terribly sorry and it will haunt me for the rest of my life," Loprais said in a video on his Facebook page.
Loprais, who turned 43 on the day of the accident, said he had had no idea what had happened at the time.
"The entire crew learnt about it when we went to bed and the commissioners came and told us they had a video recording of the accident," he said.
Loprais, whose uncle Karel Loprais won the Dakar Rally six times in the truck category, said the victim suffered a heart attack during the journey to hospital "two or three hours after" the accident.
"So a human life was wasted and I am to blame because I was driving," said Loprais.
Loprais, who was seeking his maiden victory after racing at the Dakar Rally since 2006, published a video of the accident on his Facebook page.
The rally ends on Sunday in the eastern Saudi city of Dammam.
Held in Saudi Arabia for the fourth edition in a row, the rally is raced mostly in desert areas but nevertheless attracts spectators even if in far smaller numbers than when the race was held in Africa and Latin America.