Tributes poured in Wednesday for Heath Ledger, whose sudden death was described by his Brokeback Mountain director Ang Lee as "heartbreaking" and would require further tests to explain, according to the medical examiner's office.

Heath Ledger attends a special Cinema Society screening of I'm Not There in New York in November 2007.
(Evan Agostini/Associated Press)

An initial autopsy on the late actor proved inconclusive and would require further tests, according to officials.

Ellen Borakove, a spokeswoman for the medical examiner's office, said the tests would take 10-14 days to complete.

Taiwanese filmmaker Lee directed Ledger in his Oscar-nominated turn as the gay cowboy Ennis in 2005's Brokeback Mountain and was among the flood of family, friends, colleagues and fans mourning the 28-year-old, Australian-born actor found dead at his Manhattan loft on Tuesday.

"Working with Heath was one of the purest joys of my life," Lee said. "He brought to the role of Ennis more than any of us could have imagined — a thirst for life, for love and for truth, and a vulnerability that made everyone who knew him love him. His death is heartbreaking."

Investigators said on Wednesday they found bottles of prescription sleeping pills and anti-anxiety medication in Ledger's bedroom and bathroom, echoing their earlier speculation that he had died of an accidental overdose.

In a November interview, the actor admitted to feeling stressed out during recent filming and, after having trouble sleeping, had been taking sleeping pills.

Ledger, left, won wide acclaim for his performance opposite Jake Gyllenhaal in Brokeback Mountain.
(Kimberly French/Odeon Films)

Ledger's family rejected any suggestion their son committed suicide, also calling his death accidental.

Ledger's father, Kim, read a statement Wednesday in the actor's hometown of Perth, Australia, where he spent some time during the Christmas holidays.

"We, Heath's family, can confirm the very tragic, untimely and accidental passing of our dearly loved son, brother and doting father of Matilda," Ledger said. "He was found peacefully asleep in his New York apartment by his housekeeper at 3:30 p.m."

Ledger remembered his son as a "down to earth, generous, kindhearted, life-loving, unselfish individual" who was "extremely inspirational" to those who knew him.

He also asked the media to respect the family's privacy and the need to grieve.

Larry Williams, father of actress Michelle Williams, Ledger's former partner and mother of their daughter, Matilda, extended his sympathies to the actor's family.

Early Wednesday, Williams and her daughter left Trollhattan, Sweden, where she had been shooting the upcoming film Mammoth, said a spokesman for the film's production company.

Tributes in N.Y., from fellow Aussies

As news of the death spread, a makeshift memorial of bouquets, candles and messages of condolence for the young actor was set up by mourners outside the entrance of the SoHo building where he lived. Tributes also poured in from his fellow Australians.

Actress Nicole Kidman called the death a "terrible tragedy," while Cate Blanchett, who recently starred with Ledger in the film I'm Not There, said she was "shocked and saddened."

Actor Mel Gibson, who appeared with Ledger in The Patriot, issued a statement saying that the young actor "was just taking off, and to lose his life at such a young age is a tragic loss."

Australian Prime Minister Kevin Rudd expressed shock over losing "one of our nation's finest actors in the prime of his life."

Ledger's death also prompted the White House to postpone a Wednesday event in which U.S. President George W. Bush was slated to promote an ad campaign about preventing prescription drug abuse.

"We thought it would be better to postpone the event rather than run the risk of anyone thinking that we were being opportunistic in highlighting the issue," said White House press secretary Dana Perino. 

With files from the Australian Broadcasting Corporation, the Associated Press