Lou Reed, whose band the Velvet Underground became one of the most influential in rock music, has died at the age of 71 in New York, his literary agent said.

The first Velvet Underground record sold 30,000 copies in the first five years. I think everyone who bought one of those 30,000 copies started a band. Brian Eno

Reed died on Sunday of an illness related to a May liver transplant, according to Andrew Wylie, who said the singer had been frail for months.

Born in 1942, Reed found success with the Velvet Underground in the 1960s, fusing art and music in collaboration with artist Andy Warhol and producing music that influenced generations of musicians.

"The first Velvet Underground record sold 30,000 copies in the first five years,'' Brian Eno, who produced albums by Roxy Music and Talking Heads, once said. "I think everyone who bought one of those 30,000 copies started a band.''

After leaving the Velvet Underground in 1970, Reed embarked on a solo career during which time he released the David Bowie-produced album Transformer and was thrust into rock superstardom.

While never reaching the commercial success of the Beatles and Bob Dylan, the Brooklyn-native radically expanded the territory and depth of rock lyrics.

Known as one of rock music's archetypal tough guys, Reed's trademarks were a monotone voice of uniquely emotional range and power with lyrics that were complex and controversial but maintained an intimacy with the listener.

Tributes paid

Reed was a cynic who seemed to embody the downtown Manhattan culture of the 1960s and 1970s and was as essential a New York artist as Martin Scorsese or Woody Allen.

His New York was a jaded city of drag queens, drug addicts and violence, but it was also as wondrous as any Allen comedy, with so many of Reed's songs explorations of right and wrong and quests for transcendence.

While an outlaw and controversial figure in his early years, Reed would eventually perform at the White House, have his writing published in the New Yorker, be featured by the Public Broadcasting Service in an "American Masters'' documentary and win a Grammy in 1999 for Best Long Form Music Video.

An admitted hard drinker and drug user, Reed recently had a number of health problems but remained hopeful after his liver transplant.

"I am a triumph of modern medicine, physics and chemistry," he wrote on social media. "I am bigger and stronger than stronger than ever."

Online tributes have been pouring in on social media after a message sent earlier in the day on Reed's Twitter and Facebook pages read simply, "The Door."

Punk legend Iggy Pop tweeted: "devastating news."

Reed is survived by his wife, musician Laurie Anderson who he married in 2008.