Palestinians in northern Gaza have reported fierce air and artillery strikes as Israeli troops backed by tanks pressed into the enclave with a ground assault that drew increased international calls for the protection of civilians, Reuters reports.

Israeli air strikes hit areas near Gaza City’s Shifa and Al-Quds hospitals, and Palestinian militants clashed with Israeli forces in a border area east of the city of Khan Younis, in the enclave’s south, Palestinian media reported.

There was no comment from Hamas or the Israeli military on the fighting early on Monday. Reuters was not able to confirm the reports.

The bombardments came hours after Israel released images of battle tanks on the Palestinian enclave’s western coast, signalling a potential effort to surround Gaza’s main city two days after the Israeli government ordered expanded ground incursions across its eastern border.

Some pictures posted online also appeared to show Israeli soldiers waving an Israeli flag deep inside Gaza. Reuters could not verify the images.