Martirosyan said Akasaka invited him to the exhibition's opening, but late Sunday "I was informed that the opening would be postponed, or delayed, or even canceled." He blamed Turkish "censorship" and the country's refusal "to come to terms with their own history."

  On Monday, the exhibition in the visitor's lobby had been turned around so it could not be seen by the public. Smith said he was still hoping for a diplomatic solution to the dispute.

  "We are very disappointed about it because for us, this was meant to be about the Rwandan genocide, and the lessons from the Rwandan genocide," and to engage the secretary-general on the pledge by world leaders to protect civilians from genocide, war crimes and ethnic cleansing, which Smith said was not happening in Sudan's conflict-wracked Darfur region.

  U.N. associate spokesman Farhan Haq confirmed Turkey complained about the exhibition, but he said "the basic concern" was that the review process for U.N. exhibitions, which takes into account "all positions," was not followed. He said there were other concerns which he refused to disclose.

  "The exhibition has been postponed until the regular review process is completed," Haq said.

  Smith told The Associated Press the exhibition refers to the Armenian murders to help explain the word "genocide," which was coined by Raphael Lemkin, a lawyer of Polish-Jewish descent. Lemkin was inspired by what happened to the Armenians and other mass killings, and campaigned in the League of Nations - the precursor of the United Nations.

  Turkey denies the deaths constituted genocide, saying that the toll has been inflated and that those killed were victims of civil war and unrest.

  Smith said a small panel on Lemkin in the exhibit "says that during World War I a million Armenians were murdered in Turkey." It goes on to explain that Lemkin first used the word genocide in 1943, and then focuses on the Rwanda genocide, lessons from it, and the responsibility of the international community to prevent future genocides, he said.

  Haq said "the U.N. hasn't expressed any position on incidents that took place long before the United Nations was established" after World War II.

  "In any case, the focus during the anniversary of the Rwanda genocide should remain on Rwanda itself," he said.

  Rwanda's genocide began hours after a plane carrying President Juvenal Habyarimana was mysteriously shot down as it approached the capital, Kigali, on April 6, 1994. The 100-day slaughter, in which more than 500,000 minority Tutsis were killed by Hutu extremists, ended after rebels ousted the extremist Hutu government that orchestrated the killings.

  Haq said Ban planned to meet with Rwanda's U.N. ambassador late Monday, and he read a message from the secretary-general who recalled the "personal impact" of his visit to Rwanda last year to pay his respects to victims and survivors of the genocide.

  "On this 13th anniversary of the genocide in Rwanda, two messages should be paramount," Ban said. "First, never forget. Second never stop working to prevent another genocide."