Authorities in Turkey have blocked Twitter and YouTube following a court decision on publication of images of a prosecutor killed by leftist armed men last week.

Facebook, which was reportedly blocked earlier in the day, was opened to access after removing the content in question.

YouTube.com ran the text of a court ruling on its site, saying an "administration measure" had been implemented by the country's telecommunications authority (TIB).

Bulent Kent, the secretary general of Internet Service Providers Union (ESB), said that a prosecutor's order was issued to the union, but that the process was ongoing, according to Turkish daily Hurriyet.

He said that all service providers were expected to implement the ban immediately.

Prosecutor Mehmet Selim Kiraz and his two captors linked to Marxist Revolutionary People's Liberation Party–Front (DHKP-C) died after a shootout at a courthouse in Istanbul on Tuesday.

The DHKP-C had published pictures showing one of the gunmen, his face concealed by a scarf with the group's red and yellow insignia, holding a gun to the hostage's head at his offices in Istanbul.

The images were circulated on social media while the siege was going on and were published by several Turkish newspapers as well as news websites.

A day after the standoff, Turkish prosecutors launched a probe into four newspapers for disseminating "terrorist propaganda" after they published the images in question.

Not the first time

Turkey temporarily blocked Twitter and YouTube in the run-up to local elections in March 2014, after audio recordings purportedly showing corruption in the inner circle of President Recep Tayyip Erdogan, who was prime minister at the time, were leaked to the internet. The decision caused a public uproar and drew heavy international criticism.

Turkey filed the majority of the aggregate content removal requests made to Twitter in the second half of 2014, data published in February by the micro-blogging site showed. Out of 1,982 tweets and 85 accounts withheld in the period in question, 1,820 and 62 came from Turkey, respectively.

Parliament last month approved legislation to tighten the government's control over the internet by allowing it to block websites without prior judicial authorisation, sparking outrage both at home and abroad.

The Constitutional Court, the highest judicial authority in the country, found in various 2014 verdicts that blocking social media sites as a whole violates the right to freedom of expression and "had no legal basis".

The court also annulled parts of a Turkish law on the internet that gives telecommunications authority the power to order the blocking of a URL without a court order.

Parliament last month approved similar legislation despite last year’s Constitutional Court verdicts, once again, allowing it to block websites without prior judicial authorisation.