Iran’s judiciary has blocked newly introduced voice calls on Telegram, the most popular messaging app in the country, AFP reported Wednesday, citing state media.

The blockage follows the arrest last month of 12 people who ran popular reformist channels on Telegram, ahead of next month’s presidential election in Iran.

It was not clear if the blockage of voice calls, which Telegram introduced worldwide last week, was political or designed to protect the commercial interests of domestic phone companies, noted AFP.

“We gave the authorization for the establishment of Telegram’s voice call service on Friday… but it was blocked by a judicial order,” Telecommunications Minister Mahmoud Vaezi was quoted as having told reformist newspaper Shargh.

“You should ask the judiciary for the reason,” he added.

Iran is notorious for the limitations it imposes on freedom of expression. The country blocks access to numerous websites, including Facebook and Twitter, in order to stop Iranians from browsing content it considers immoral, or as undermining the regime.

Last month, the conservative-dominated judiciary blocked the online navigation app Waze because it was designed in Israel, which Iran does not recognize.

In addition to blocking messaging apps, the Islamic Republic regularly detains journalists who are deemed to be against the government.

Iranian officials have previously said there were around 20 million Telegram users in the country, which has a population of some 80 million.

As well as a messaging tool, Telegram has become the leading source of news for many Iranians, with some channels boasting more than a million subscribers.

Iranian President Hassan Rouhani, who has been often touted by the West as a “moderate”, has criticized the arrests but has little power over the judiciary.