Activists and experts who monitor the Twitter traffic of the Islamic State and its supporters noticed something odd last week when many accounts suddenly disappeared.

The activists exchanged messages about the missing accounts, suspecting they had been suspended.

On Thursday, a Twitter representative confirmed what some were saying and put a number on it. The social media network’s violations department suspended approximately 10,000 accounts on April 2 “for tweeting violent threats,” the representative said.

It was impossible to independently verify the assertion because Twitter’s data is not public. But it would be the biggest single mass purge by Twitter of accounts linked to the Islamic State, also known as ISIS, ISIL and Daesh, which some experts believe has as many as 90,000 affiliated accounts.

The suspensions came against a backdrop of rising criticism that Twitter has allowed the Islamic State to exploit the social network to spread propaganda, glorify violence and seek recruits.