The Israeli military has said a tank fired at three Palestinian children who were killed in Gaza on Tuesday because troops mistook them for militants.

The three cousins - two boys aged 10 and 12, and a 12-year-old girl - were playing near rocket launchers outside Beit Hanun, a military statement said.

An internal army investigation found soldiers had detected "unidentified movement and opened fire", it added.

The army initially said militants had sent the children to get the launchers.

Both the Israeli military and Palestinian witnesses have said children have been used to retrieve launchers after rockets have been fired.

But army aerial surveillance videos of the incident proved the children were simply playing tag.

"They were playing right next to the launchers, including touching them," the army statement said.

The soldiers used the aerial video to direct the tank fire, the army said.

"At the very last second, it was apparent that they were children, but it was impossible to stop the explosion," it added.