Turkey's NTV television said an initial forensic report concludes that the nine activists killed in the Israeli commando raid on the aid flotilla to Gaza died of gunshot wounds.
The station cited medical sources. It said the forensic report came after the bodies were examined at an Istanbul morgue on Thursday.
Monday's raid had also left several injured. They are being treated at Turkish hospitals.
Meanwhile, the head of an Islamic group that organized the pro-Palestinian aid flotilla to Gaza claimed the beating of some Israeli soldiers during a deadly raid was self defense.
Bulent Yildirim, who arrived in Istanbul early Thursday after being deported from Israel along with hundreds of others from the boats, said activists also had seized weapons from some Israeli soldiers, but threw them into the sea. He said the activists attacked the Israeli commandos with chairs and sticks in self defense.
Israel has said two of the seven soldiers wounded were shot with guns that were wrested from them, while a third was stabbed.
"Even if we had used the guns that would be still a legitimate self defense," said Yildirim, a lawyer, accusing Israel of raiding the ships in international waters on Monday.
The activists maintain their flotilla aimed to break a three-year blockade that Israel has imposed on the Gaza Strip to carry food and other supplies to the Palestinians who live there.
Israel has contested that, saying the sticks, iron bars and knives that the passengers allegedly used in the shipdeck battle showed their purpose was not humanitarian.
'They faced barbarism and oppression'
Yildirim vowed to organize bigger convoys by land and sea if Israel does not end the blockade of Gaza.
Israel's Prime Minister Benjamin Netanyahu late Wednesday hotly rejected calls to lift the blockade on Hamas-ruled Gaza, insisting the ban prevents missile attacks on Israel. He labeled worldwide criticism of his country's raid on the flotilla as "hypocrisy."
"This was not the 'Love Boat,'" Netanyahu said in an address to the nation. "It was a hate boat."
Serkan Nergis, a spokesman for the charity group, the IHH, said Thursday that charity workers and relatives were now trying to identify five of the bodies of those killed in the raid at an Istanbul morgue. Four of them have been officially confirmed to be Turks.
A total of 466 activists, including more than 50 foreigners, returned to a hero's welcome with thousands of supporters waving Palestinian flags and chanting "God is Great!" in Istanbul.
"Turkey is proud of you!" the crowd chanted as they shouted "Down with Israel!"
Deputy Prime Minister Bulent Arinc welcomed the activists at the Istanbul airport after Turkey pressured Israel to release the detainees, most of whom are Turkish. Others were from Arab countries, Europe and the United States.
"They faced barbarism and oppression but returned with pride," Arinc said.
Turkish Ambassador Oguz Celikkol, whom Turkey recalled to protest the Israeli raid on the Turkish ship, also returned to Istanbul on Thursday.
The activists were taken to a state forensic institute to be questioned and undergo medical tests, to ensure the activists were not harmed and to collect evidence for possible legal action against Israel.
"We felt it necessary. Because we may seek justice within international laws and we may need certain evidence in doing so," Arinc said. "It may be possible that they (the activists) may have been given certain medicines or similar substances while in Israel. The test results will determine this."
Turkey's state-run Anatolia news agency said prosecutors were expected to question 19 injured activists who were being treated in a hospital in the capital, Ankara.