ANKARA, Turkey (AP) -- Access to jailed Istanbul mayor Ekrem Imamoglu 's social media account on X has been blocked in Turkey, a monitoring platform said Thursday, the latest move against a key rival to President Recep Tayyip Erdogan.

According to Engelli Web, a website that that tracks and reports internet censorship in Turkey, X restricted Imamoglu's account in Turkey complying with a legal request by Turkish authorities who cited national security and public order concerns.

There was no immediate comment from X but a notice on the platform says the account -- which has 9.7 million followers -- has been "withheld in TR in response to a legal demand." The account remains accessible outside of Turkey.

Imamoglu, seen as the main opposition challenger to Erdogan's 22-year rule, was arrested on March 19 and jailed on corruption charges. He was nominated as his Republican People's Party, or CHP's presidential candidate while in custody.

His arrest has been widely viewed as politically motivated although the government insists Turkey's judiciary is independent and free of political influence. It triggered widespread demonstrations calling for his release and an end to Turkey's democratic backsliding under Erdogan.

Despite his detention, Imamoglu had remained active on social media. His lawyers are expected to appeal the legal restriction.

Opposition politicians criticized the restriction as an assault attack on free speech in Turkey.