Tony Stewart pulls out of NASCAR race

According to authorities and eye-witness accounts, the three-time NASCAR Sprint Cup Series champion hit and killed fellow driver Kevin Ward Jr. who had walked towards Stewart's car after the two had an altercation during a race at Canandaigua Motorsports Park.

The Ontario County (N.Y.) Sheriff"s Office confirmed in a news release that Ward Jr. had been declared dead 45 minutes after the incident upon arrival at Thompson Hospital.

Some reports suggested Stewart would still take part in Sunday's NASCAR race in Watkins Glen, New York, but Stewart-Haas Racing vice president of competition Greg Zipadelli has now confirmed the 43-year-old's withdrawal.

"It's just an unbelievable tragedy," Zipadelli said. "Our hearts go out to Kevin and his family. Thoughts and prayers.

"This is a very tough, very emotional time for everybody - his family, our family at Stewart-Haas, Tony Stewart.

"With that being said, we feel that as a group, Tony will not drive.

"We gave Tony some time to sleep on it and met with him this morning and he feels strongly that this is the right thing to do."

Nationwide Series driver Regan Smith will deputise for Stewart behind the wheel of the number 14 Chevrolet.

In relation to Saturday's tragedy, Sheriff Philip C. Povero had earlier told reporters: "Right now, this is an on-track crash investigation. There are no criminal charges pending at this time. We are not making any inferences of any criminal conduct at all.

"He [Stewart] was visibly shaken by this incident and promised his continuing cooperation of this investigation."