Greek singer Demis Roussos, best known for his hit operatic pop ballads in the 1970s and 1980s, has died aged 68.

Roussos died in Athens at the weekend, Igia Clinic, the medical facility where he was being treated, said on Monday.

A public funeral is to take place on Friday at the First Cemetery of Athens, a resting place for many Greek politicians and cultural figures.

Roussos, who was famous for his high-pitched voice and melodies inspired by Greek folklore, sold about 60 million records worldwide.

The pop star was briefly held hostage by Lebanese militants in 1985 when he was aboard a hijacked plane in Greece.

Roussos was born in Egypt on June 15, 1946 to a Greek father who was forced to take the family back to Greece in 1961 in the midst of the Suez Canal crisis.

He shot to fame in the 1970s after teaming up with fellow Greek musician Vangelis in the band Aphrodite's Child.

'Made country proud'

He soon went solo and built a long career over which he sold millions of albums with such hits as "Forever and Ever", "Mr Reason", "Goodbye My Love, Goodbye" and "Quand je t'aime."

"Along with Nana Mouskouri, he is one of the two biggest Greek pop music artists. They are the two great voices that put Greece on the map," French-Greek TV personality Nikos Aliagas told the AFP news agency.

"We had known each other since I was a kid. He broke through borders and made his country proud," Aliagas added.

Roussos had long struggled with his weight, but he later trimmed down and even penned a diet book called "A Question of Weight". In subsequent years the singer suffered ill-health that kept him chair-bound.

He recorded and toured until 2009, when he released his last album. One of his last public appearances was in Athens in 2013, when he received the Legion of Honour - France's highest distinction - for his life's work.

But it was his melancholy face on 1970s and 1980s album covers that provided the most enduring image of the singer: a theatrical figure with a flowing dark beard, intense dark eyes and long hair thinning on top.

He carried this larger-than-life persona on stage with colourful clothing, and sustained it with a voice that belted out powerful operatic flourishes.