Funeral prayers take place for the nine pro-Palestinian activists flown home on Thursday.
Prayers for the eight Turkish victims of Israel's maritime attack.
Chanting anti-Israeli slogans, thousands of mourners thronged Istanbul's Faith Mosque.
The ninth victim of Monday's raid on the Turkish-backed aid flotilla was an American of Turkish origin.
The killings of Turks has outraged the Muslim country.
And ties between the Jewish state and Turkey's Islamist-leaning government are close to breaking point.
Eyewitness accounts are still emerging as activists aboard the Gaza-bound aid flotilla return to Europe.
In Rome, Italian activist Manuel Zani described how the mood of the Israeli soldiers became increasingly brutal.
"Little by little as we were being held (by Israeli forces) they were less tolerant and became more angry. People were hit after any type of protest. Several people, not from our boat, got onto the plane bleeding or wearing bandages because they were beaten at the airport."
Israel defends the commando raid as self defence, insisting its forces were attacked first.
The assault has strengthened calls for Israel's blockade of Gaza to be lifted immediately.
Fiona Cameron, Reuters