Major US social media companies including Meta’s Facebook and Instagram platforms have blocked the accounts of Saudi Arabian dissidents so they are no longer visible inside the kingdom, following orders by Saudi authorities.

Those affected include Abdullah Alaoudh, a US-based activist and vocal critic of Saudi human rights violations, and Omar Abdulaziz, a Canada and UK-based activist who worked closely with Jamal Khashoggi before the journalist’s murder by Saudi agents in 2018.

At least seven accounts had been blocked by Meta at the end of April, including those of two American citizens and two individuals based in Europe, according to the advocacy group American Committee for Middle East Rights (ACMER).

Alaoudh, who serves as ACMER’s senior policy adviser, said: “Meta is effectively doing Saudi Arabia’s dirty work against Americans living in the United States. When a company geo-blocks accounts on behalf of a government with a documented record of silencing dissent, it becomes an instrument of repression. Meta should push back.”

Meta did not respond to the “dirty work” claim, but provided a statement to the Guardian saying that when “something happens” on one of its platforms that is reported as violating local law but not the companies’ own community standards, the company may restrict the content’s availability in the country where it is alleged to be unlawful.

It added that “in a majority of cases” it informs affected users which state authorities sent the requests.

Meta operates a public “transparency centre”, where it acknowledges that Saudi authorities contacted the company and sought restrictions on a total of 144 Instagram accounts, Facebook pages, and Facebook profiles during April. The site also shows that Meta restricted access to 108 “items”.

Interviews with some of the dissidents targeted suggest the companies approached by Saudi authorities did not all respond in the same way.

While Meta did alert users that their content was being blocked due to a “local legal requirement, or a request from a government”, Snapchat appears to have slowed or removed accounts in Saudi Arabia – including one used by Abdulaziz – without alerting the account owners of the change.

It is not clear how many Snapchat accounts were affected, and its owner, Snap Inc, declined to comment.

At least two users of X, which is owned by Elon Musk, received letters informing them that the platform had received a request from the Saudi communications, space and technology commission claiming their accounts violated Saudi laws.

A Saudi decree attached to the letters and seen by the Guardian said the accounts transmitted material that “infringes on public order, religious values, public morals, or the sanctity of private life”.

X told users including Abdulaziz that it had not taken any action on the reported content yet, writing that the company “strongly believes in defending and respecting the voice of our users”. It then urged addressees to seek legal advice if they wished, or to delete the relevant content voluntarily.

X did not respond to a request for comment.

Abdulaziz told the Guardian: “I think this is just the introduction to a massive crackdown by the Saudi government to mute opposition. It could go as far as committing atrocities, just like they did with the murder of Jamal Khashoggi.”

The Saudi government did not respond to a request for comment, sent through the Saudi embassy in Washington.

Other accounts targeted include those of individuals linked to the London-based human rights organisation ALQST, including its founder, Yahya Assiri. It said the requests from Saudi Arabia did not represent a neutral legal process, but instead exposed how authoritarian censorship can be dressed up as procedure.

“These [account holders] are not dangerous actors; they are people documenting abuses, challenging state propaganda and giving voice to Saudis inside the country who cannot speak freely,” said Dr Maryam Aldossari, an ALQST board member.

“Blocking these accounts would not protect public safety, it would project authoritarian power from scrutiny. X cannot hide behind vague references to ‘local legal requirements’ when those laws are routinely used to criminalise peaceful dissent.

“This is how authoritarian censorship travels: through legal notices, platform pressure and the attempted outsourcing of repression to global technology companies.”