Thirty-one premature babies were evacuated from Gaza's biggest hospital Sunday, the World Health Organization has said, seeking to get the last patients and staff out of what it has dubbed a "death zone."

The evacuation came as Israel, which said it was stepping up military operations against Hamas militants, announced it had found a 55-meter tunnel under the Shifa hospital and released footage it said showed "hostages" inside the facility.

The developments, as sirens blared across Jerusalem to warn of rocket fire while Israel intensified air strikes on Gaza City, came as Qatar said "minor" obstacles remained for a deal on the release of hostages.