Activists in Iran are expressing concern about widespread internet outages and residents being unable to access social media.
Anger has circulated online after over a week of protests sparked by the death of a Kurdish woman in police custody.
Internet monitoring group NetBlocks said Instagram and WhatsApp - two of the major communication tools that Iran usually allows - had been restricted.
WhatsApp said it was working to keep Iranian users connected.
The two Meta-owned apps have millions of Iranian users and have become increasingly popular after authorities blocked other platforms in recent years, including Facebook and Twitter.
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The latest intermittent blackouts follow the eruption of nationwide protests over Mahsa Amini's death. The 22-year-old had been detained for allegedly failing to adhere to hijab (headscarf) rules.
NetBlocks reported that the internet was partially reconnected on Thursday night but that on Friday it was suffering a "nation-scale loss of connectivity" again.
"People in Iran are being cut off from online apps and services," Instagram chief Adam Mosseri tweeted, adding that "we hope their right to be online will be reinstated quickly".
But others accused Meta of being complicit in disconnecting users.