Turkish authorities have pressed to block access to YouTube following similar action against Twitter, a move sure to provoke further outrage in a country where social media is widely used.
Turkey's technology minister, Fikri Isik, on Thursday (local time) said the national telecommunications authority was imposing the block "as a precaution" after an audio recording of a government security meeting was leaked on the video-sharing website.
Despite the government's actions, YouTube was still widely accessible following the announcement.
Key allies, including the US and the European Union, had criticised Turkey's earlier move against Twitter as a restriction of free speech and a step backward for Turkish democracy. That ban came shortly after Prime Minister Recep Tayyip Erdogan threatened to "rip out the roots" of Twitter, which has been a conduit for links to recordings suggesting government corruption.
Turkey holds crucial local elections on Sunday that are widely regarded as a referendum on Erdogan's rule.
The ban against YouTube comes after an alleged audio recording of a meeting between the Turkey's foreign minister, intelligence chief and top military and Foreign Ministry officials was leaked on YouTube. The four are allegedly heard discussing a military intervention in neighbouring Syria, a sensitive political issue in Turkey, although the context of the conversation is not clear.
A Foreign Ministry statement said the meeting was held to discuss threats of a possible attack on a mausoleum in Syria - of the grandfather of the Ottoman Empire's founder - which is considered Turkish territory and protected by Turkish troops.
A government official said access to YouTube was closed down out of "national security concerns and because of the urgency of the situation." The official said the move aimed to prevent the "posting of other recordings that may threaten national security." The official spoke on condition of anonymity because of government rules that bar civil servants from speaking to journalists without authorisation.
Erdogan railed against the audio leak.
"This is immoral, this is sleaze, this is shameful, this is dishonourable," he said during a campaign rally.
Foreign Minister Ahmet Davutoglu called the leak an act of espionage and an "open declaration of war against the Turkish republic". In a statement, his office called eavesdropping on a top-secret meeting an attack on Turkey's security and said those responsible would be severely punished.
The state-run Anadolu Agency reported that a chief prosecutor had launched an investigation into possible espionage over the YouTube leak and the country's media watchdog imposed a news blackout on the details of the recording.
Google owns YouTube and Google spokeswoman Abbi Tatton said some users in Turkey weren't able to access YouTube.
"There is no technical issue on our side and we're looking into the situation," she said.
The US-based firm Renesys confirmed a partial blocking of YouTube while the number of tweets mentioning Turkey and YouTube had multiplied several times on Twitter, according to the social media monitoring firm Brandwatch.
In a tweet, European Commission Vice President Neelie Kroes called the block against YouTube "another desperate and depressing move in Turkey".
"I express my support for all those supporters of real freedom and democracy," she said. "We in Europe stand for an open internet and free expression on it."
The government's attempted crackdown on Twitter came after links to other wiretapped recordings suggesting corruption were spread on the microblogging site, causing Erdogan's government major embarrassment before Sunday's election.
Erdogan has confirmed that he personally ordered the block on Twitter, alleging that the company wasn't following Turkish laws. Despite the block, many Turkish users have found ways to access Twitter.
Erdogan has blamed a movement led by US-based moderate Islamic cleric Fethullah Gulen, a former political ally of Erdogan, for the leaks.
Also on Thursday, a television station linked to Gulen said Turkish authorities had withdrawn its license to broadcast nationally.