Hamas is preparing to strike Israel using a unit of specialist commando divers, the Israel Defence Force's Lieutenant Colonel Asaf Hamami has told Israel's Army Radio. During the July 2014 conflict between Israel and Hamas, four Hamas frogmen militants were killed in a gun battle with Israeli forces on Zikim Beach, north of the Gaza Strip, after reaching the Israeli coast undetected.

In response, Israel put in place the Aquashield defence system, which identifies divers near strategic Israeli coastal positions by means of underwater cameras and sensors.

Hamami has said that the Hamas frogman squad was still planning to attack Israel, and that it had expanded since 2014. "We see them in training, their entire range of training, including diving and shooting."

Hamas, the militant Islamist group which governs the Gaza Strip, is believed to have built a network of tunnels to infiltrate Israel and transport weapons and fighters around Gaza. In March 2016, the IDF announced it had discovered a cross-border tunnel in southern Gaza.

In the Army Radio interview Navy Squadron Commander Lieutenant Colonel Liav Silverman referred to the underwater threat from Hamas as the underwater 'blue tunnel' threat.

"Any attempt by the enemy to develop the capacity for diving and sailing, is challenging above and under water," he told the station.

In August, 2015, Hamas announced that it had captured an Israeli spy dolphin, equipped with devices including cameras, off the coast of Gaza, local media has reported. Palestine's Al Quds newspaper claimed that the dolphin had been turned into a "murderer" by Israeli security services, and the capture showed the extent of Israel's "anger" and "indignation" at the formation of Hamas's naval combat units.

In February, 2015, Israel Hayom reported that the Aqua Shield system – manufactured by Israel's DSIT Solutions – had been installed along the sea border with the Gaza Strip, and was being installed along Israel's northern sea border.

A picture taken from the beach in the southern Israeli kibbutz of Zikim shows the skyline of Gaza City
A picture taken from the beach in the southern Israeli kibbutz of Zikim shows the skyline of Gaza CityGetty