Fifteen ships will leave for Gaza from various Mediterranean ports around June 20, he added.
Some 1,500 activists from about 100 countries will board the vessels, which will also carry humanitarian aid, medical equipment, school supplies and construction materials, including up to 700 tonnes of cement, said Huseyin Oruc, a senior member of the Turkish Islamist charity IHH.
The activists made the remarks during a press conference on board the Turkish ferry Mavi Marmara to mark the first anniversary of the bloody ending to the ship's first mission to break Gaza's blockade.
Nine Turkish activists were killed on May 31 last year when Israeli forces stormed the Mavi Marmara, which was the lead ship of an international convoy spearheaded by the IHH.
The raid in international waters triggered worldwide condemnation and plunged Turkish-Israeli ties into a deep crisis.
Turkish and foreign activists held a march in downtown Istanbul on Monday evening to commemorate the nine dead, drawing an estimated 10,000 people, an AFP correspondent reported.
"Wait Palestine, the Mavi Marmara is coming" read one of the many banners written in Turkish, Hebrew and English, held by the marchers as they made their way down the main commercial boulevard of Istanbul.
On Saturday Egypt reopened its Rafah border crossing with Gaza, allowing people to cross freely for the first time in four years and giving Gazans a gateway to the world.
Rafah is the only crossing which does not pass through Israel.
The boats in the new mission, coming from Canada, France, Greece, Ireland, Italy, Spain, Turkey and the United States, would meet in international waters south of Cyprus before heading to Gaza, Oruc said.
Asked whether the activists would again use iron bars and bats to resist an eventual Israeli raid, he said: "We do not believe that they will repeat the same big mistake... The activists will sail peacefully."
Israeli-Swedish musician Dror Feiler added: "What will happen will depend on the Israelis: if they choose the path of peace, it will be peaceful. If they choose the path of violence, unfortunately it will be violent but we will not be violent."
IHH chairman Bulent Yildirim said the flotilla would be open to an international inspection to certify that the activists are not armed and that their cargo does not include weapons.
"Any international commission can search the ships. We would be pleased if this happens as we are fed up with Israeli propaganda," Yildirim said on Turkey's NTV television.
Israel had said after last year's raid that some passengers were armed, a claim denied by activists.
Turkey has warned Israel against another bloodshed, saying it "would give the necessary response to any repeated act of provocation by Israel in high seas."
The one-time allies remain stuck in crisis after several fence-mending meetings failed to yield results.
Turkey, which has recalled its ambassador from Tel Aviv, insists the Jewish state should apologise and compensate the victims' families.