Academics and writers in Turkey have risked a fierce official backlash by issuing a public apology for the alleged genocide suffered by Armenians at the hands of Ottoman forces during the first world war.

Breaking one of Turkish society's biggest taboos, the apology comes in an open letter that invites Turks to sign an online petition supporting its sentiments.

It reads: "My conscience does not accept the insensitivity showed to and the denial of the Great Catastrophe that the Ottoman Armenians were subjected to in 1915. I reject this injustice and for my share, I empathise with the feelings and pain of my Armenian brothers. I apologise to them."

The contents expose its authors - three scholars, Ahmet Insel, Baskin Oran and Cengiz Aktar, and a journalist, Ali Bayramoglu - to the wrath of the Turkish state, which has prosecuted writers, including the Nobel prize-winning novelist Orhan Pamuk, for supporting Armenian genocide claims.

Turkey rejects the assertion of many historians and Armenia's government that up to 1.5 million Armenians died in a wave of expulsions that amounted to state-sanctioned genocide. Officials claim the death toll was much lower and that most of the victims died from disease. They also say many Turks were killed by Armenians, who have long been accused of allying themselves with enemy Russian forces against the Ottoman empire.

The letter has triggered a furious response from ultranationalists, who have labelled it a "betrayal" and an "insult to the Turkish nation".

However, Aktar, a professor of EU studies at Istanbul's University of Bahcesehir, said Turks needed to apologise for being unable to discuss the issue because of official policy, which has long repressed open debate on the Armenians' fate.

"Today many people in Turkey, with all good intentions, think that nothing happened to the Armenians," he told the newspaper Vatan. "The official history says that this incident happened through secondary, not very important, and even mutual massacres. They push the idea that it was an ordinary incident explainable by the conditions of the first world war. Unfortunately, the facts are very different."

He added: "This is a voice coming from the individual's conscience. Those who want to apologise can apologise, and those who do not should not."

The letter coincides with a tentative rapprochement between Turkey and Armenia.

In September, the Turkish president, Abdullah Gul, attended a football match between the two countries, at the invitation of his Armenian counterpart, Serge Sarkisian.

But further talks aimed at restoring ties have become bogged down partly because of Armenian reluctance to accept a Turkish demand for a joint commission to investigate the genocide claims.