Image copyright Twitter Image caption A message posted on Amnesty International's Twitter account

Twitter accounts, including Amnesty International, Unicef USA and BBC North America, have been hacked by attackers claiming to back Turkey's government.

The hackers tweeted in Turkish including the words "Nazi Germany, Nazi Holland", and posted the Turkish flag.

It echoes comments by Turkish President Recep Tayyip Erdogan who compared German and Dutch officials to Nazis, in a diplomatic row.

Twitter says it has located and removed the source of the hacking attack.

A company spokesperson is quoted as saying that the source had been tracked to a third party app whose permissions had been removed.

The spokesperson provided no further details.

Amnesty International said on Twitter: "Earlier this morning our Twitter account was hacked." It added it was now investigating what had happened.

BBC North America stated in a tweet: "Hi everyone - we temporarily lost control of this account, but normal service has resumed. Thanks."

The hackers also targeted business publisher Forbes, government agencies and celebrities.

The messages posted on some of the accounts included the phrase "see you on 16 April" - an apparent reference to the Turkish referendum set for that date.

The row between Turkey and the German and Dutch governments escalated after the two EU members banned public rallies involving Turkish ministers.

The ministers had been due to address people of Turkish descent ahead of April's referendum on expanding presidential powers.