Spanish opera singer Montserrat Caballe, who was renowned for her bel canto technique and her interpretations of the roles of Rossini, Bellini and Donizetti, died yesterday at the age of 85.

Hospital Sant Pau spokesman Abraham del Moral said Caballe's family requested that the cause of death was not revealed, however she had been in the Barcelona hospital since September.

Spanish media said that Caballe entered the hospital in September because of a gall bladder problem.

The song Barcelona, Caballe's duet with Freddie Mercury, was a hit single in 1987 and became the anthem of the 1992 Summer Olympics in the city.

Spanish prime minister Pedro Sanchez said: "A great ambassador of our country has died. Her voice and tenderness will remain with us forever."

King Felipe VI tweeted that Caballe was "the great lady of opera, legend of universal culture, the best of the best" and that "her personality and unequalled voice will accompany us forever".

Tenor Jose Carreras said opera had lost its "best soprano", adding: "Of all the sopranos that I have heard live, I have never heard anyone like Montserrat."

She was born Maria de Montserrat Viviana Concepcion Caballe i Folch into a working class family in Barcelona. Caballe unveiled her musical talents early, singing Bach cantatas at the age of seven.

In her almost unlimited repertoire, she starred in 90 opera roles with nearly 4,000 stage performances.

At the age of eight, Caballe entered Liceo's Conservatory in Barcelona with Eugenia Kenny, Conchita Badea and Napoleone Annovazzi among her first teachers.

She won the school's Gold Medal on graduating in 1954, and went on to study opera in Milan and in 1956 joined the Basel Opera and played her first major role that year in the city's Staatstheater as Mimi in Puccini's La Boheme.

Four years later, she was a principal singer with the Bremen Opera.

In 1964, she married Spanish tenor Bernabe Marti. They had two children, Bernabe Marti Jr and Montserrat Marti, herself a successful soprano.

In the year she was married, Caballe gave a highly praised performance of Jules Masenet's Manon in Mexico City, but it was a year later in New York that a lucky break launched her on the road to international stardom.

On short notice, she stood in for indisposed American soprano Marilyn Horne in a concert performance in Donizetti's Lucrezia Borgia at New York's Carnegie Hall and achieved a thunderous success. It opened the doors to all the major opera venues around the world.

She produced a highly acclaimed performance as Elisabetta of Valois in an all-star cast of Verdi's Don Carlo at the Arena di Verona in 1969. The concert became famous for her "la" on the final "ah" at the end of the opera, which lasted for more than 20 bars up, driving the audience wild with delight.

Caballe was also a noted recitalist, particularly of songs of her native Spain. She was particularly admired for her purity of voice, vocal shadings and exquisite pianissimos.

In 1997, she sang on two tracks on an album by New Age composer Vangelis. In 1999 Cabale performed Barcelona live, accompanied by a recording of the late Mercury, at the Champions League football final in Barcelona's Camp Nou stadium.

In 2015, Caballe was convicted of tax fraud and given a suspended sentence of six months in prison. She had failed to pay the Spanish treasury more than 500,000 euros in taxes on her earnings.

Caballe dedicated herself to various charities and was a Unesco Goodwill Ambassador. She also established a foundation for underprivileged children in Barcelona.