Twitter shut down  at least half a dozen accounts after they were revealed to contain disturbing images of child abuse, according to a report in the Daily Mail.

Graphic pictures  became public last night after “hacking groups claimed to have broken into private accounts to expose their indecent content, ” the newspaper reported, citing the NSPCC, a British charity devoted to ending cruelty to children in the U.K.

The Child Exploitation and Online Protection Centre  (CEOP) also received about 30 reports of similar images relating to at least four Twitter accounts, the Daily Mail reported, adding that it remains unclear whether the images were distributed by British users of Twitter or from outside the country. The nationality of the children in the images also is unknown.

The cases will be investigated in the U.S., where Twitter is based. Twitter is required by law to send details of any accounts containing indecent images of children to the U.S.-based National Center for Missing and Exploited Children NCMEC), which will ”forward information for investigation to law enforcement agencies in the relevant country where the user is believed to be based, or children believed to be at risk,” a spokesperson for the CEOP told the Daily Mail.

Twitter has apparently issued a response to anyone contacting the company over the images of alleged abuse, according to the Daily Mail. This reads: “We do not tolerate child pornography on Twitter. When we are made aware of such images they will be removed from the site without further notice.”