Michael Jackson, the "King of Pop," has died after suffering cardiac arrest at his Los Angeles home. The singer had been preparing for a major comeback after years of seclusion.

A fire department official said Jackson was not breathing when paramedics arrived at his rented Bel Air mansion at 12:26 p.m. It's believed his personal physician was with him at the time.

Jackson, 50, was then treated at UCLA Medical Center, just a six-minute drive away. But hospital officials were unable to revive him. His brother Jermaine Jackson said doctors pronounced him dead at 2:26 p.m.

"A team of doctors, including emergency physicians and cardiologists, attempted to resuscitate him for a period of more than one hour. And they were unsuccessful," he told reporters.

Jermaine Jackson also asked media to respect his family's privacy "during this tough time, and may all love be with Michael always."

The circumstances of Jackson's death were not immediately clear. Ed Winter, the assistant chief coroner of the Los Angeles County coroner's office, said he would handle the investigation.

Because of Jackson's high profile, the Los Angeles Police Department has also assigned two robbery-homicide detectives to the case, but said there was no evidence of criminal wrongdoing.

"Don't read anything into it," LAPD Lt. Gregg Strenk told reporters.

Lawyer Brian Oxman, a sometime-spokesperson for the Jackson family, alleged that prescription medications may have contributed to the death.

"For the last many months, and almost more than a year, this family has been talking about the use of medications by Michael and warning he was going to wake up dead," Oxman, his voice wavering, told CTV News Channel. "This was our fear."

Jackson's death came as he prepared for a major comeback next month, after years of seclusion. He was scheduled to perform 50 shows in London's O2 Arena, with the financial backing of two billionaires.

Jackson, who had won 13 Grammys and sold more than 750 million albums over his career, had not embarked on a major tour since 1997.

In recent years, he had been the subject of endless tabloid headlines and financial difficulties. If his London shows had proved successful, he was expected to embark on a major world-wide series of concerts.

He first gained fame as a musical prodigy with his brothers in the Jackson 5. He was just a child, but under the watchful eye of his father, Joe Jackson, the group managed a string of hit singles with Motown Records.

The singer then broke out on his own in 1971, and began to craft his reputation as the "King of Pop." His solo efforts have become some of the best-selling albums of all time, including "Off the Wall," "Thriller" and "Bad."

The latter two albums coincided with the rise of MTV, and Jackson became known for a series of ground-breaking music videos -- including the horror-themed "Thriller."

Along with his talents as a singer and songwriter, he was also a spectacular dancer. He showed off his signature move, "The Moonwalk," during a 1983 television appearance celebrating the 25th anniversary of Motown.

But as his fame rose, so did his eccentricity. He became known for his child-like demeanor and his treasure trove of toys and amusement park rides at his Neverland Ranch -- named after the fantastical island of Peter Pan.

By the late-1980s he had become fodder for the tabloids. In 1986, it was erroneously reported that he slept in a hyperbaric chamber. Other reports focused on his paling skin, which Jackson blamed on the disease Vitiligo, and his numerous plastic surgeries that completely changed his facial appearance.

And then in 1993, in the most severe blow to his career, Jackson was accused of child molestation. He eventually settled the allegations out of court, but they continued to haunt him and the public never saw Jackson the same way again.

In 2005, he was again accused of child molestation. He denied all charges and was acquitted in court.

This past year, Jackson's financial problems appeared to have escalated to the point where he was ready to auction off more than 1,000 personal items -- including a few of his trademark single gloves.

But in April, Jackson filed a legal action to stop the auction.

The March announcement of 50 shows at London's O2 Arena appeared to signal a return to form for Jackson, and a way to settle his debt problems. Tickets for the event, called "This is It," sold out within hours.

"I love you," Jackson had told fans during the announcement. "I really do. You have to know that I love you so much. Really, from the bottom of my heart."

Jackson leaves behind three children: Prince Michael, 7, Michael Joseph Jackson Jr., 12, and daughter Paris Michael Katherine, 11.