The military says the ship, Klos C, was carrying Syrian-made M-302 rockets. It was intercepted more than 1,000 miles (1,600 kilometers) south of Israel off of Sudan and Eritrea.
The military says the M-302 rockets have a range of up to 100 miles (160 kilometers) and would have significantly improved the capabilities of Gaza militants, putting nearly all of Israel in their range. It said the operation followed months of intelligence gathering.
Israel accuses Iran of supplying rockets and other arms to its foes and has seized ships carrying weapons in the past.