To any western viewer it would have been the most normal thing in the world: a TV programme showing a group of musicians performing and playing live in the studio.

But viewers in Iran found themselves rubbing their eyes in disbelief when the morning programme broadcast the musicians playing traditional Persian instruments, because for many it was the first time they had seen such instruments on national television.

Although the Islamic republic of Iran Broadcasting (IRIB) tolerates non-western music – albeit to an extent – and singers are regular guests there, musical instruments have been banned on state TV for more than three decades.

But on Saturday Avaye Parsian (Persian voice), led by musician Saman Alipour, were filmed in the studio of the Good Morning Iran show for IRIB's Channel 1 playing santoor, a trapezoid-shaped Persian dulcimer played by wooden hammers, tar (Iranian lute) and kamancheh, a bowed string instrument.

On previous occasions when bands have been invited to perform on state television only the singer would be allowed to go in front of cameras – musicians would play backstage or the screen would cut to flowers and beautiful landscapes. A recent ceremony broadcast live on the IRIB was cut when a musician began to play piano.

Astonished viewers quickly took pictures of their television screens with their cellphones when they saw Alipour's band, who had been invited to perform in celebration of Prophet Muhammad's birthday the next day.

"Am I dreaming or what?" tweeted one Iranian, posting an image he took from his screen. On Monday the reformist Shargh daily published the image, which by then had circulated all over the internet among Iranian users, on its front page.

"Musical instruments on Channel 1," read the headline along with a screenshot of the state TV programme with the timeframe showing 8:44:44. "The [state] TV's green light [to musical instruments] took viewers by surprise," said Shargh's front page.

"The programme invited us to go to their studio for a live performance and as usual we went there with our instruments but we didn't expect the instruments to be shown," Alipour told Shargh. "When the time came for our section of the programme, they asked us to be seated in front of cameras."

Iranian users on Facebook and Twitter welcomed the ground-breaking incident and shared images they captured of the performance. Saturday's incident strengthened hopes among many that it would mean a long-standing ban was about to expire as president Hassan Rouhani opens up to the world and relaxes social restrictions at home. But the welcome it received seems to have backfired with the programme's producers, saying it was a mistake.

"We invited the band but because of a mistake on our part, for 10 seconds people could see the instruments. It was our mistake and it doesn't show any change in the IRIB's internal policy," Good Morning Iran's producer, Gholamreza Bakhtiari, told the semi-official Fars news agency.

Iran does not allow private TV and radio channels in the country but tens of Iranian channels run by exiles are available via illegal satellite dishes on rooftops, including the BBC's Persian services. Many Iranians find the IRIB's restrictive policy ridiculous because Persian culture is entwined with poetry and music. Students take music courses at universities and millions take private classes to learn music as a hobby.

Iran's supreme leader, Ayatollah Ali Khamenei, who has the final say on all state matters, is sceptical of music and advises against practising or teaching it in the country. "Although music is halal, promoting and teaching it is not compatible with the highest values of the sacred regime of the Islamic Republic," he said in response to a request for a religious ruling in 2010. His ruling, however, is not fully enforced.

Iranian artists, including the grand-maestro Mohammad Reza Shajarian and composer Hossein Alizadeh have been outspoken in their criticism of the IRIB's restrictive policies. And earlier this week a group of young musicians from a band called Pallett made their own stand against the ban. When they were invited to perform on the IRIB, they decided to mime playing the musical instruments.