Hamas said on Saturday its militants did not intend to target Israeli schoolchildren when they fired a rocket at a bus two days ago, critically wounding a teenager and sparking the latest round of border fighting.

"It was not known that the bus targeted on the outskirts of Gaza carried schoolchildren," spokesman Sami Abu Zuhri told Reuters, adding that the road where the bus was travelling was often used by Israeli military vehicles.

Israel has maintained that the bus, because it was yellow, should have been easy to identify by whoever fired the anti-tank rocket. Prime Minister Benjamin Netanyahu has accused the Islamist Hamas, which rules Gaza, of "crossing a line".