Robert Menard spoke to reporters in Tunis via a mobile phone
Reporters Without Frontiers (RSF) head Robert Menard said Tunisian security officials had not allowed him to leave the plane after his arrival from Paris.
Tunisia said it had acted because of pending legal action against him.
Delegates at the summit also accused the Tunisian hosts of sending hecklers to a debate on freedom of speech.
The Tunisian government denies the accusations.
The North African country has been condemned for the way it filters websites in an academic study released to coincide with the World Summit on the Information Society (WSIS), which opened on Wednesday.
The conference is looking at ways of combating poverty through increased use of information and communication technologies.
But the UN has tried to overcome widespread criticism of its choice of venue, saying the summit will shed light on the situation in Tunisia and may even improve it, the BBC's Pascal Harter in Tunis reports.
'Internet's enemies'
Mr Menard said that he had been prevented by Tunisian security officials from leaving his aircraft seat.
The RSF blacklisted 15 countries on its map
"I have all my papers in order to enter the country, a passport and an accreditation number for the WSIS, and they are telling me I can't come in," Mr Menard was quoted as saying in a phone call to reporters.
Tunisia have repeatedly said that Mr Menard was "subject to a legal injunction" in France under which he can enter the country only with the permission of a magistrate.
The UN International Telecommunications Union, which is organising the summit, said pending legal action following incidents in Paris in 2002 meant that Mr Menard could not benefit from the immunity granted to summit participants.
At the summit, the RSF unrolled a banner condemning 15 countries it called "enemies of the internet" because they filtered out access to websites.
The group listed Belarus, China, Cuba, Iran, Libya, the Maldives, Myanmar, Nepal, North Korea, Saudi Arabia, Syria, Turkmenistan, Tunisia, Uzbekistan and Vietnam.
The government of President Zine El Abidine Ben Ali rejects any suggestion that it violates human rights or limits legitimate access to traditional or electronic media.
'Focused filtering'
But a study by the OpenNet Initiative found that nearly 10% of the 2,000 sites it had tested from within the country were blocked.
They were mostly sites devoted to political opposition, human rights, pornography and tools to circumvent the country's controls.
The OpenNet Initiative is university collaboration between Toronto, Harvard and Cambridge.
"Tunisia's internet filtering is focused, effective, and deceptive," said the report's co-author Derek Bambauer, who is a fellow at Harvard Law School's Berkman Center for Internet and Society.
The  World Summit on the Information Society, organized by the International Telecommunication Union, concluded on Friday evening, November 18th, in Tunis, the capital of the north African nation of Tunisia. The event's organizers intended for the event to "put into motion" the plan for Internet financing and governance developed at the 2003 WSIS summit in Geneva, Switzerland.

The summit was marred by criticism of Tunisia for allowing attacks on journalists and human rights defenders to occur in the days leading up to the event. A French journalist for "Libération" was stabbed and beaten by unidentified men after he reported on local human rights protesters. A Belgian television crew was harassed and forced to hand over footage of Tunisian dissidents, while local human rights defenders were roughed up and prevented from organising a meeting with international civil society groups. A representative from the French media watchdog Reporters Without Borders, Robert Menard, was prevented from disembarking from his Air France flight to Tunis to attend the summit.

''Expression Under Repression panel at WSIS in Tunis.Source: Rebecca MacKinnon''

During the event, representatives from the Global Voices project were menaced by the Tunisian police as they held their session on "Expression Under Repression." Speaking at the session were Rebecca MacKinnon, Ethan Zuckerman, Nart Villeneuve, Taurai Maduna, Isaac Mao, and Hossein Derakshan, among others. The  interaction with the Tunisian police is related by Amanda Michel of the Berkman Center with the description from an attendee as, "Before the break, a phalanx of secret police (ie scary guys in dark suits) showed up. They filled the hall outside the room, forcing cancellation of the break for fear that we'd not be allowed to re-start."

Nicholas Negroponte demonstrated the first working prototype of his $100 laptop.