Israeli forces launched heavy airstrikes on Gaza City and surrounding areas overnight Wednesday into Thursday, a day after announcing the start of “preliminary operations” aimed at taking control of the city, fueling growing international concern over the worsening humanitarian crisis in the besieged enclave.

The Israeli government on Wednesday approved a military plan to seize Gaza City and announced the call-up of around 60,000 reservists starting in early September.

“We are not waiting. Our forces have already begun preliminary operations and are positioned on the outskirts of Gaza City,” the army said in a statement.

The announcement sparked international criticism as well as domestic opposition, with warnings that the escalation could further exacerbate the suffering of over two million Palestinians in the blockaded territory.