The popular micro-blogging site, one of several that has been used to publish allegations of corruption in Prime Minister Recep Tayyip Erdogan's inner circle, went dark in Turkey yesterday, just hours after the embattled leader threatened to "wipe out" the social network.
The move sparked outrage from the opposition and the European Union -- which Ankara has long sought to join as well as Erdogan's own administration.
Turkish President Abdullah Gul, a frequent user of social media, led the chorus of calls against the move.
"A complete ban on social media platforms cannot be approved," he said, adding that it is not "technically possible to totally block access to platforms used all over the world".
Opposition lawmaker Aykan Erdemir said his party would take "legal action" against the ban, warning that the move would put Turkey into a league of undemocratic countries like China.
"This is an unbelievable violation of fundamental rights and freedoms," Erdemir, of the Republican People's Party (CHP), said.
European leaders said the move violated citizen's rights to freedom of speech and could threaten Turkey's bid to enter the 28-nation bloc. Ankara is already the world's top jailer of journalists, according to press freedom lobby group The Committee to Protect Journalists.
"The ban on the social platform Twitter.com in Turkey raises grave concerns and casts doubt on Turkey's stated commitment to European values and standards," EU Enlargement Commissioner Stefan Fule said in a statement.
"Social media has a vital role to play in a modern democracy. As a candidate country, EU expects Turkey to promote the values of freedom of expression, democracy and the rule of law," tweeted Britain's embassy in Turkey.