YouTube attracts a monthly audience of 70 million people

The ban was imposed after prosecutors told the court that clips insulting former Turkish leader Mustafa Kemal Ataturk had appeared on the site.

According to Turkish media, there has been a "virtual war" between Greek and Turkish users of the site, with both sides posting insulting videos.

The clip prompting the ban reportedly dubbed Ataturk and Turks homosexuals.

Insulting Ataturk, the founding father of modern Turkey, or "Turkishness" is an offence which can result in a prison sentence.

The offending videos sparked a storm of complaints to YouTube and the clips were removed, but the court order goes further, blocking all access to the site.

Freedom of speech

Turkish visitors to the site are now greeted with a message in English and Turkish reading "Access to www.youtube.com site has been suspended in accordance with decision no: 2007/384 dated 06.03.2007 of Istanbul First Criminal Peace Court".

Paul Doany, the head of Turk Telecom, the country's largest telecoms company, said that they had blocked access to the site as soon as the court order came through.

"We are not in the position of saying that what YouTube did was an insult, that it was right or wrong," Mr Doany told Anatolia news agency. "A court decision was proposed to us, and we are doing what that court decision says."

Mr Doany said that for its part Turk Telecom will continue to enforce the ban as long as the order stands.

The European Union, which Turkey is hoping to join, has long called for an easing of Article 301 - the law which prevents insults to Turkish culture - arguing that the law places severe restrictions on free speech in Turkey.

About 50 writers in the country have been put on trial for allegedly contravening the rule, including Nobel prizewinner Orhan Pamuk, though most cases have eventually been dismissed by the judge.