A Turkish government minister for the first time attended a mass Friday to mark the 1915 massacres of Armenians in Istanbul as President Recep Tayyip Erdogan repeated his "condolences" to the victims' descendants.

"We respect the suffering of our Armenian brothers, that is why we have come to take part in this ceremony," European affairs minister Volkan Bozkir told the press, as a message in Armenian and English from Erdogan was read to the congregation at a solemn ceremony marking the centenary at the Armenian Patriarchate in the city.

Erdogan -- who last year first expressed his sorrow over the "shared pain" of the slaughter -- said in the message that "our hearts remain wide open to the grandchildren of the Ottoman Armenians all around the world".

More than 100 people also gathered outside the former Ottoman capital's old prison -- now a museum of Islamic art -- where Armenian leaders and intellectuals were taken on April 25, 1915, in what was has come to be seen as the start of the killings.

Many held placards in Turkish, Armenian and English urging Ankara to recognise the killings as genocide, and recited the names of Armenian villages which were destroyed on the orders of Ottoman officials.

"I wanted to come here, to the middle of the Turkish people, to commemorate this common cause," activist Satenik Baghdasaryan, who had come from the Armenian capital Yerevan, told AFP.

"It is my way of showing my recognition of the work that they (human rights groups in Turkey) have done to push their government to recognise what happened," she added.

Turkey hotly disputes labelling the massacres carried out during World War I a genocide, claiming almost as many Muslim Turks died in the chaos of the conflict in eastern Anatolia.

"We expect the Turkish state to recognise the genocide and to stop putting the denial at the heart of its education system, diplomacy and politics," said Benjamin Abtan, of the European Grassroots Antiracist Movement, which helped organise the protest.

Despite the huge international pressure it has come under in recent days, Turkish leaders seem no closer to officially conceding that the killings amounted to genocide.

Prime Minister Ahmet Davutoglu earlier this week dismissed much of the efforts as a "racist" attempt to denigrate Turkey.

However, he said Turks "share the pain of the grandchildren and children of Ottoman Armenians who lost their lives during deportation in 1915.

"(But) to reduce everything to a single word, to put responsibility through generalisations on the Turkish nation alone... is legally and morally problematic," he added.