"This was not a humanitarian sail, but a violent provocation directed against us," said Israel Defense Forces Spokesperson Avi Benayahu. "We were attacked with clubs and long knives."
According to an initial military report, at least 10 activists who took part in the sail were killed and several were injured.
Arab media provided conflicting reports on the casualties, some stating that 15 people were killed and 50 were injured.
According to an IDF source, "The sail's participants were not innocent and used violence against the soldiers. They were waiting for the forces' arrival."
According to Benayahu, "Our forces encountered serious violence, nearly unprecedented. Throughout the night, we continued the diplomatic effort through the communication methods in the sea.
"The Navy commander took charge of the event from a command post in the sea. He ensured that the six ships received warnings to turn back and an invitation to sail to the Ashdod Port to complete the delivery of the aid through land crossings after an Israeli security check. In all these cases we were firmly turned down."
'Near lynch against soldiers'
According to the IDF spokesperson, the army received an order to stop the boats which were carrying unknown equipment. "In the largest boat, called 'Marmara', there are 570 people. The fighters, who arrived with ladders and came down from ropes, encountered what they described as a near lynch.
"There was serious violence, cols arms, knives, we have a stabbed soldier, clubs. You can see that every soldier that came down was attacked. This is not the activity of peace activists."
Benyahu confirmed that the activists snatched one of the fighters' weapons. "He was attacked by the crowd and they opened fire. During the incident, our fighters were in real danger, both from the clubs and from the weapons. They used crowd dispersal means, and when there was no choice – live ammunition. We don't know if there were any other weapons on the ship, because the entire picture is unclear. We did not encounter peace activists on this boat."
Shmulik Grossman, Roni Sofer, Yoav Zitun, Ali Waked and Roee Nahmias contributed to this report