Iran International did not breach the broadcasting code by interviewing a spokesman for a separatist group who praised last September’s terrorist attack in the Iranian city of Ahvaz, the British regulator Ofcom has ruled.

The news channel, which broadcasts in Farsi but is based west London, interviewed Yacoub Hor al-Tostari, a spokesman for the Arab Struggle Movement for the Liberation of Ahvaz in the immediate aftermath of the attack on a military parade which left 30 people dead, and which was later condemned by the UN security council as a “heinous and cowardly terrorist attack”.

During the interview al-Tostari justified the killings, which he said had hit “legitimate” military targets. Iran’s ambassador to the UK was among those who filed an official complaint to the broadcast regulator over Iran International’s decision to broadcast the interview.

However, following an investigation Ofcom concluded the channel did provide sufficiently strong context to “justify the potentially high level of offence” that could have been caused by the broadcast of al-Tostari’s statements supporting the attack.

According to the regulator, Iran International’s presenter “clearly challenged his views and emphasised the violent nature of the attack” during the interview.

The channel also included a number of different viewpoints and repeatedly quoted news agencies describing the terrorist nature of the incident.

Ofcom concluded the UK broadcasting code code does not prohibit particular people from appearing on television and radio services just because their views or actions have the potential to cause offence: “To do so would, in our view, be a disproportionate restriction of the broadcaster’s right to freedom of expression and the audience’s right to receive information and ideas.”

Iran International’s representatives said the channel “provides fair, balanced and impartial coverage, and abides by its published Editorial Guidelines”, adding that it “covers the widest range of opinions of interest to all Iranians and Farsi speakers”.

It also said that although privately owned “it is a public service news channel, and takes its responsibilities very seriously” and that included the spokesperson’s interview represented “a significant and important insight into the separatist movement in Khuzestan”.

The channel’s licence owner said that all of its senior journalists “have worked for organisations like the BBC, renowned production companies, or reputable newspapers or websites. They are neither pro nor anti regime.”

It added that it had received a positive overall response on the coverage of the attack and that “any criticism emanated from the Iranian government or its publications or known supporters”.

“The Ofcom ruling says that the coverage was legitimate and a valid area for discussion,” said Rob Beynon of DMA Media, the company which runs Iran International.