Access to the social media account of Istanbul's jailed opposition mayor, Ekrem Imamoglu, has been blocked by the authorities in Turkey, BBC reports.

Imamoglu, who is the main rival to President Recep Tayyip Erdogan, can no longer send messages in Turkey to his 9.7 million followers on X. But his account is still accessible abroad.

His social media feed has been his main tool for communicating with his supporters and keeping himself in the public eye.

He had been posting daily by sending messages out from prison via his lawyers.

Opinion polls suggest that Ekrem Imamoglu, who has been elected mayor of Turkey's largest city three times, would win a presidential election if he was able to stand.

The next presidential election is not due to be held until 2028.

A message on his account on Thursday said it had been blocked due to a legal demand, although it is still available in Turkey with the use of a virtual private network (VPN).

A lawyer representing X said he had filed a court challenge to the ban, at the request of the social media platform.

Istanbul prosecutors are investigating a post on Imamoglu's account, on the basis that it may constitute an incitement to commit crime, according to the president's communications office.

In that post last month, the mayor condemned his arrest and a wider crackdown on the opposition and called on the nation to complain and "raise your voice.”