An outspoken critic of Russian president Vladimir Putin has been prevented from addressing a major international conference in Northern Ireland, organisers claimed.
Russian journalist Oksana Chelysheva was due to give a keynote address at the Poisonous Legacies event in Londonderry on Saturday but was stopped on arrival at Stansted Airport.
Conference organiser Paul O'Connor said the journalist, who has been openly critical of the Russian premier's handling of the conflict in Chechnya, was detained for six hours before being sent back to her home in Finland.
"She did not arrive as planned last night," said Mr O'Connor.
"Why wasn't she allowed in? We are asking the question why was an esteemed, award-winning journalist recognised by Amnesty International not allowed to enter the country?
"We will now have an empty chair where someone was supposed to be talking about the situation in Chechnya - it does not reflect well."
Mr Putin is due to join the leaders of the world's richest countries for the G8 summit in Co Fermanagh next week.
Ms Chelysheva, who won Amnesty International's Special Award for Human Rights Journalism Under Threat in 2006, has been campaigning for a war crimes tribunal to deal with the Chechen conflict.
The Poisonous Legacies conference, organised by the Bloody Sunday Trust and the Pat Finucane Centre, will examine the impact of conflict and colonialism in various parts of the world, including the Middle East, Colombia, Argentina, Chechnya, Spain, Italy and Ireland.
It coincides with the third anniversary of the publication of the Saville Report into the killing of 13 civil rights marchers in Derry in January 1972 by members of the Parachute Regiment and is part of the Derry/Londonderry UK City of Culture 2013 programme.