Israeli forces battling Hamas said they had uncovered an unusually large concrete and iron-girded tunnel, designed to carry carloads of militant fighters from Gaza right up to the border, writes Reuters.

Razing or disabling hundreds of km of underground passages and bunkers is among the aims of the offensive Israel launched after Hamas gunmen went on a killing and kidnapping spree in its southern towns and army bases on Oct. 7.

Among sites that Hamas overran in that attack was the Erez border crossing between Gaza and Israel. Just 100 metres (yards) south of the checkpoint, concealed in a sand dune, the military showed reporters the exit point of what it said was a flagship Hamas project.

The tunnel ran down diagonally to a depth of 50 metres, where it expanded to a relatively capacious 3 metres in height and width, with electrical fittings.

Chief military spokesperson Rear Admiral Daniel Hagari put the full length of the tunnel at 4 km - enough to reach into northern Gaza City, once the heart of Hamas governance and now a devastated combat zone.

“It was the biggest tunnel we found in Gaza ... meant to target the (Erez) crossing. Millions of dollars were invested in this tunnel. It took years to build this tunnel ... Vehicles could drive through”, - Hagari said.

Hamas did not respond to a Reuters request for comment on the Israeli account.