Israeli tanks have blocked the main road to Gaza City, preventing those who have left the besieged city from returning, and Defence Minister Israel Katz said it was now the last chance for hundreds of thousands of people still inside to escape, Reuters reports.

Israel has told the entire million-strong population of Gaza City to head south as it mounts one of the biggest offensives this month, vowing to root out Hamas fighters in what it alleges are their last bastions in Gaza’s biggest urban area.

Residents told Reuters that tanks had set up sand barriers on the main road south out of Gaza City. People were being allowed out, but those who had left in search of food or temporary shelter were no longer being permitted to return.

“This is the last opportunity for Gaza residents who wish to do so to move south and leave Hamas operatives isolated in Gaza City itself in the face of the IDF’s continuing full-scale operations,” Israeli Defence Minister Katz said in a statement.

Those leaving would be subjected to vetting by the military, Katz said.