Egypt has blocked the encrypted messaging service Signal used by many activists and journalists in the country, the company that owns the app said.

Since Saturday, many users of the app in Egypt have complained of being unable to use the messaging system that allows exchanges with a very high level of confidentiality.

"We've been investigating over the weekend, and have confirmed that Egypt is censoring access to Signal," Open Whisper Systems wrote on its Twitter account.

"We'll begin deploying censorship circumvention in Signal over the next several weeks. Until then, Tor or a VPN can be used to access Signal," it tweeted on Monday.

The authorities in Egypt were not immediately available for comment.

Access to the internet and mobile telephone networks was blocked in the country during demonstrations that toppled longtime autocratic president Hosni Mubarak in 2011.

Since the army dismissed Islamist president Mohamed Morsi in July 2013, the authorities have suppressed all forms of opposition in a crackdown that has also targeted journalists and human rights defenders.