The regulator can force corrections, impose fines and ultimately revoke a broadcast licence, although the move would be a last resort.
It found the RT news channel broke broadcasting rules by failing to preserve due impartiality in seven news and current affairs programmes over a six-week period.
Ofcom noted that all the programmes were broadcast in the aftermath of the poisoning of Sergei Skripal in Salisbury and said it marked a “significant increase” in potential breaches during the period.
The programmes, aired between 17 March and 26 April, included two hosted by former Respect MP George Galloway, three current affairs shows and two news bulletins.
An Ofcom spokesperson said: “Our investigations found that RT failed to maintain due impartiality in seven news and current affairs programmes over a six-week period.
“Taken together, these breaches represent a serious failure to comply with our broadcasting rules.
“We have told RT that we are minded to consider imposing a statutory sanction for these breaches. The broadcaster now has the opportunity to make representations to us, which we will consider before proceeding further.”
Ofcom previously announced that it would consider whether the channel should broadcast in the UK if Russian involvement was proven in the attack on Mr Skripal, which later resulted in a British woman’s death.
Earlier this year, the regulator said it had written to RT to explain that evidence of unlawful state interference would affect whether it was deemed “fit and proper” to hold a broadcasting licence.
It later announced a wave of new investigations into the channel, which is owned by Russian state media arm TV Novosti, over impartiality.
The UK has accused Russia of proposing “contradictory and changing fantasies” to deny involvement in the attack on Mr Skripal, amid heightened tensions over wars in Syria and Ukraine, alleged election interference and cyberattacks.
Peter Wilson, Britain’s permanent representative to the Organisation for the Prohibition of Chemical Weapons (OPCW), said a “brazen disinformation campaign” was underway in April.
“They have sought to confuse, distract and brazenly misrepresent facts, despite the thorough, independent OPCW report,” that confirmed novichok nerve agent was used, he said.
RT has an average audience of 3,400 viewers at any given point during the day and an average weekly reach of one per cent of UK adults, according to Ofcom figures.
Owner TV Novosti has been disciplined for 15 breaches of the broadcasting code since 2012, which Ofcom said was not an unusually high number, but most related to Russia’s foreign policy in programmes on the wars in Ukraine and Syria.
Ofcom’s code states that all news must be reported “with due accuracy and presented with due impartiality”, and that “undue prominence” must not be given to a particular side on matters of controversy.
A spokesperson for RT said: “RT is extremely disappointed by Ofcom’s conclusions in what were almost all self-initiated investigations into RT by the regulator.
“We operate under rules outlined by the regulator, and always strive to abide by them. It appears Ofcom has failed to fully take on-board what we said in response to its investigations and, in particular, has not paid due regard to the rights of a broadcaster and the audience.
“We are reviewing the findings Ofcom has put forward and will decide shortly the nature of our next steps.”
The first programme found to be in breach was the Sputnik programme hosted by Mr Galloway on 17 March.
His co-presenter claimed that a version of novichok was held at Britain’s Porton Down defence laboratory, while a former FSB secret service officer called the poisoning a “badly prepared provocation”.
RT told Ofcom that its audience would “expect to be given a Russian perspective” on the attack, but the regulator said Mr Galloway and his co-presenter did not challenge the claims but rather “encouraged or reinforced” them.
Ofcom also rejected RT’s claim that a rolling news ticker referencing a statement from the UK, US and France did not create impartiality because it was shown only for a few seconds at a time.
A second episode of Sputnik was found in breach on 7 April, where Mr Galloway interviewed an “independent researcher” who presented the Salisbury poisoning as a plot to “punish Russia”.
Three episodes of the Crosstalk current affairs programme were also found to be in breach.
On 13 April, an episode broadcast claims of a “false flag chemical attack” in Syria and alleged the US was trying to “partition” the country and funding jihadis.
Another episode of Crosstalk on 16 April saw US-led airstrikes on alleged chemical weapons sites in Syria called a “gross violation of international law” and repeated claims that gas attacks on civilians had been “staged”.
In the third edition of Crosstalk in breach, from 20 April a presenter asked whether Washington was deliberately trying to partition Syria or “stick it to Iran and Russia”, while calling massacres using chemical weapons “false-flag operations”.
An RT news bulletin on 18 March was found to have broken impartiality rules after claiming that militants were “preparing to stage chemical attacks in Syria to give the US a pretext to attack the government”.
On 29 April, another RT news bulletin claimed that the Ukrainian government was “promoting the glorification of Nazism”.
Three further programmes were found not in breach of Ofcom’s impartiality rules.
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies