Comedy legend Robin Williams was found dead in the bedroom of his home near San Francisco with a belt around his neck and slight wounds to his wrist, police said Tuesday.

With an investigation still underway, the Marin County Sheriff's Office said suicide remains the apparent cause of death for the 63-year-old Oscar-winning actor, who had been grappling with severe depression.

"His life ended due to asphyxia due to hanging," said Lieutenant Keith Boyd, the county's assistant coroner, as tributes to Williams -- one of finest comedy talents of his generation -- poured in from around the world.

Williams was found Monday by his personal assistant "in a seated position unresponsive with a belt secured around his neck with the other end of the belt wedged between the clothes closet door and the door frame.

"Mr. Williams, at that time, was cool to the touch with rigor mortis present in his body," Boyd told reporters, adding that the inside of Williams' left wrist bore superficial cuts.

No word on suicide note

Boyd refused to say whether a suicide note was found, but he disclosed that a pocket knife with signs of dried blood on its blade was being examined.

He also said the final cause of death would not be declared until toxicology tests are completed.

Williams -- star of such hit films as "Good Will Hunting," "Good Morning Vietnam" and "Mrs Doubtfire" -- had last been seen alive Sunday by his wife Susan Schneider before she retired for the night, he said.

She left the house on Monday assuming he was still asleep in a separate room in the house in the town of Tiburon, just north of San Francisco.

Williams was found dead by his personal assistant, who entered the room "when he failed to respond to knocks on his bedroom door," Boyd said.

First responders arrived at the Spanish-style gated residence around noon (1700 GMT) Monday following a 911 emergency call from a "distraught" caller who Boyd did not identify.

Wrestled with drink, drugs

Father-of-three Williams, who wedded Schneider, his third wife, in 2011, had himself spoken openly in the past about his battles with alcoholism and drug abuse -- and often drew on them in his stand-up comedy routines.

"I love you. I miss you. I'll try to keep looking up," Williams' daughter Zelda said in an Instagram message that appeared alongside a quote from "The Little Prince" by French writer and aviator Antoine de Saint-Exupery.

President Barack Obama led public tributes to an entertainer he described as "one of a kind," while Hollywood titan Steven Spielberg hailed Williams, a close friend, as a "lightning storm of comic genius."

Fans worldwide united in grief via social media, with #RobinWilliams trending on Twitter throughout the day.

Minatare shrines popped up at Williams star on Hollywood's Walk of Fame, a park bench in Boston that featured in "Good Will Hunting" and the Victorian house in Colorado where his breakthrough 1970s space alien sitcom "Mork and Mindy" was recorded.

"He was a giant heart, a fireball friend, a wondrous gift from the gods," said British actor, director and Monty Python alum Terry Gilliam. "Now the selfish bastards have taken him back."