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Twitter is suing Turkey after Ankara fined the social media giant for not removing content deemed by the Turkish government to be "terrorist propaganda".

The lawsuit comes after the Turkish Information and Communication Technologies Authority imposed a $50,000 fine on Twitter for failing to comply with requests to remove content.

A Turkish official quoted by Reuters on Thursday said that much of the material in question was related to the Kurdistan Workers' Party (PKK), which is listed as a terrorist organisation by Turkey, the US and the EU.

Turkey has previously pursued aggressive internet censorship policies and banned Facebook, YouTube, Reddit and Twitter.

In April 2015, Facebook, Twitter and YouTube were all briefly blocked after they refused to take down photos of a prosecutor who had been taken hostage by leftist militants in Istanbul and later died of his injuries.

Eight hours after the order, the websites complied and the ban was revoked.

YouTube was also banned for two months in 2014, before Turkey's highest court ruled that the ban violated laws on freedom of expression.

Everyone will see how powerful the Republic of Turkey is

Turkish President Recep Tayyip Erdogan has had several run-ins with social media sites, saying in March 2014 that Twitter would be "eradicated", should it not comply with Turkish court orders - and that such platforms would be "wiped out".

"The international community can say this, can say that," Erdogan said at a rally at the time. "I don't care at all. Everyone will see how powerful the Republic of Turkey is."

Turkey has some of the highest censorship requests submitted to Twitter and requested information on 670 users in the first half of 2015, according to .

However, this is the first time that Turkey has imposed a financial fine on a social media company for refusing to comply with its censorship requests.

Twitter is arguing that the fine is illegal under Turkish law, according to the official quoted by Reuters.