Turkey's president led the country's Twitter users in defying a government ban on the social networking site that has been condemned by world leaders.
Opposition leaders said they would mount a legal challenge to the ban on the popular site, one of several that has been used to publish allegations of corruption in Prime Minister Recep Tayyip Erdogan's inner circle.
Turkish President Abdullah Gul, a frequent user of social media, led the chorus of calls against the move, which comes days ahead of key local elections on March 30.
Government officials including Deputy Prime Minister Bulent Arinc also flouted the ban as Turks took to the Internet to vent their fury.
"A complete ban on social media platforms cannot be approved," tweeted Gul, adding that it is not "technically possible to totally block access to platforms used all over the world".
Twitter went dark in Turkey late Thursday. But tweets from Turkey, which has 10 million users, were up 138 percent on Friday afternoon compared to Wednesday, according to social media analysts Brandwatch.
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), told AFP.
Twitter responded by saying on its official @policy feed that Turks could get around the block by tweeting through mobile telephone text services.
A lawyer acting for Twitter held talks with the telecommunications authority on Friday, a Turkish official told AFP. Local media said the US company had hired Gonenc Gurkaynak to challenge the ban.
Online, outraged Twitter users shared details of how to get around the ban, including using "virtual private networks" to make it appear as though they were accessing the site from another country.
Hashtags #TwitterisblockedinTurkey and #TurkeyBlockedTwitter trended across the network.
- 'Shocking' ban criticised -
In Washington, State Department spokeswoman Jen Psaki said the order to prevent Turks from accessing Twitter was "contrary to Turkey's own expressed desire to be a model of democracy."
"We urge the Turkish government to unblock its citizens' access to Twitter and ensure free access to all social media platforms," she said.
She added that she was not aware of any moves by the US administration to play a role in reported negotiations between the US owner of Twitter and the Turkish government.
European leaders said the move violated citizens' rights to freedom of speech and could threaten Turkey's bid to enter the 28-nation European Union.
"The ban... raises grave concerns and casts doubt on Turkey's stated commitment to European values and standards," EU Enlargement Commissioner Stefan Fuele said in a statement.
France labelled the move "shocking" and "contrary to the freedom of expression and communication which are fundamental principles" of the EU.
Britain's embassy in Turkey called on Ankara to reverse the decision, while a spokesman for German Chancellor Angela Merkel tweeted that "in a free society it is up to citizens to decide how to communicate, not the state".
The ban on Twitter is the latest in a series of moves by Erdogan's government to tighten its control of the Internet that have included the banning of thousands of websites.
Many Turks have turned to Twitter and Facebook to express their outrage since anti-government protests last year, complaining that mainstream media is under government pressure.
Turkey is the world's top jailer of journalists and dozens have been sacked or forced to resign since the violent clashes, according to journalists' unions.
Early this month, Erdogan warned that his government could ban Youtube and Facebook after the local polls. YouTube was banned for two years up to 2010.
"These measures are devastating to free expression and freedom of the media and they curb citizens' right to freely express themselves," said OSCE Representative on Freedom of the Media Dunja Mijatovic.
The restriction of access to Twitter came after Erdogan told an election rally in western Bursa Thursday that he would "wipe out Twitter" in defiance of international criticism.
His office said that authorities would "technically block access to Twitter" because the service had ignored Turkish court orders to get rid of illegal links.
- Graft allegations tweeted -
Erdogan, Turkey's leader since 2003, has come under mounting pressure since audio recordings were published that appeared to put him at the heart of a major corruption scandal.
They included an apparent discussion between Erdogan and his son about hiding money, and others in which he appears to be interfering in business deals, court cases and media coverage.
Some of the most damaging information has come from a Twitter account named Haramzadeler ("Sons of Thieves"), which has published documents and police wiretaps allegedly linked to the investigation.
Erdogan has dismissed most of the recordings as "vile" fakes concocted by his rivals, including former staunch ally US-exiled cleric Fethullah Gulen.
Dozens of people have been arrested as part of the probe, including four ministers and other key Erdogan rivals. Gulen has denied any involvement.