Thousands of people have rallied in Istanbul to protest at the murder of a prominent Turkish-Armenian journalist, Hrant Dink, outside his office.
Dink's murder has provoked widespread shock in Turkey
"We are all Armenians, we are all Hrant Dink," the crowd chanted.
Dink frequently wrote about one of the most sensitive issues in Turkey - the mass killing of Armenians during the final days of the Ottoman empire.
His views, seen as treachery by some nationalists, led to a conviction in 2005 for insulting Turkish identity.
"A bullet has been fired at democracy and freedom of expression," Turkish Prime Minister Recep Tayyip Erdogan told a hastily convened news conference as news of Dink's murder spread.
The attack on Dink was an attack on Turkey and on Turkish unity and stability, Mr Erdogan said, adding that the "dark hands" behind the killing would be brought to justice.
The murder is likely to increase political tensions in Turkey, where politicians have been courting the nationalist vote ahead of presidential and parliamentary elections later this year, correspondents say.
Police said Dink, 53, was shot at least twice. Turkey's NTV television showed pictures of a white sheet covering the journalist's body in front of the newspaper building's entrance.
Late on Friday, Turkish media quoted Istanbul's governor as saying three people were in custody in connection with the killing.
Journalists and politicians in Turkey expressed outrage at the killing, which many described as a political assassination, while the US, EU, Armenia, and several human rights groups also voiced shock and condemnation.
A crowd of several thousand people marched towards the office of Agos, the bilingual Turkish and Armenian weekly newspaper Dink edited, on Friday night.
Many carried red carnations and photographs of Dink with the inscription "My dear brother" in Turkish, Armenian and English.
The mood was not sombre but angry, the BBC's Sarah Rainsford reports from Istanbul, with many demanding justice. There was also a protest by several hundred people in Ankara.
Dink was one of Turkey's most prominent Armenian voices and despite threats on his life, he refused to stay silent.
"I will not leave this country. If I go I would feel I was leaving alone the people struggling for democracy...It would be a betrayal of them," he told Reuters news agency last July.
Dink was found guilty in October 2005 of insulting Turkish identity after he wrote an article which addressed the mass killings of Ottoman Armenians nine decades ago.
He always said his aim was to improve the difficult relationship between Turks and Armenians.
Dink was gunned down in broad daylight
In his last newspaper column, he wrote that there was a considerable group of people "who see me as an enemy of the Turks," and said he had received letters "full of anger and menace."
Dink was among dozens of writers in Turkey who have been charged under article 301 of Turkey's penal code with insulting Turkish identity, often for articles dealing with the killing of Kurds and Ottoman Armenians.
Hundreds of thousands of Armenians died in 1915, in what Armenians say was a systematic massacre at the hands of the Ottoman Turks.
More than a dozen countries, various international bodies and many Western historians have recognised it as genocide.
Turkey denies any genocide, saying the deaths were a part of World War I.
Turkey and neighbouring Armenia still have no official relations.