ISTANBUL – Thousands of mourners hailed activists killed in an Israeli commando mission as martyrs Thursday, hoisting their coffins to cheers of “God is great.”

Turkish leaders said Israel had jeopardized its relationship with its closest Muslim ally despite meeting Ankara’s demand to release the hundreds captured in the raid.

The father of the youngest of the nine activists killed — 19-year-old high school student Furkan Dogan, who had dual U.S.-Turkish citizenship — praised his son for dying in a just cause.

Ahmet Dogan told the state-run Anatolia news agency he identified his son in the morgue and he had been shot through the forehead. Still, he said, the family was not sad because they believed Furkan had died with honor.

“I feel my son has been blessed with heaven,” he said. “I am hoping to be a father worthy of my son.”

Dogan, who was born in Troy, N.Y., but moved to Turkey when he was 2, was to be buried in his family’s hometown of Kayseri in central Turkey on Friday.

He was one of eight activists mourned at the massive funeral in Istanbul, which came as Israel rejected demands for an international panel to investigate its deadly takeover Monday of six aid ships trying to break Israel’s three-year blockade of the Gaza Strip. Israeli Prime Minister Benjamin Netanyahu has hotly rejected calls to lift the blockade on Hamas-ruled Gaza, insisting it prevents missile attacks on Israel.

The incident has increased tensions in the Mideast, especially with Turkey, an important ally of Israel. On Thursday, Prime Minister Recep Tayyip Erdogan called Israel’s actions “a historic mistake.”

“Israel risks losing its most important friend in the region if it doesn’t change its mentality,” he said.

President Abdullah Gul said Israel committed “one of the biggest mistakes ever in its history.”

“Turkey will never forget this attack,” Gul said. “The relations between Israel and Turkey will never be the same again.”

At Thursday’s funeral, 10,000 people prayed outside Istanbul’s Fatih mosque before eight flag-draped coffins holding Dogan and seven Turks. A ninth victim, a Turkish man, was to have a separate service today.

“Let them do what they want, we know how to be martyrs for Palestine and Jerusalem, and that’s what we became,” said Bulent Yildirim, the head of the Islamic charity group IHH, which organized the Gaza flotilla.