Israel fired artillery and mounted more air strikes on Friday against Palestinian militants in the Gaza Strip amid constant rocket fire deep into Israel’s commercial center.

As hostilities entered their fifth day, with no sign of abating, the Israeli military said in a statement shortly after midnight that air and ground forces were attacking the Hamas-run enclave. Rocket barrages from Gaza swiftly followed.

Although the statement gave no further details, Israeli military affairs correspondents who are briefed regularly by the armed forces said it was not a ground invasion, and that troops were firing artillery from Israel’s side of the border.

Residents of northern Gaza, near the Israeli frontier, said they had seen no sign of Israeli ground forces inside the enclave but reported heavy artillery fire and dozens of air strikes.

Israeli Prime Minister Benjamin Netanyahu said on Thursday the campaign “will take more time”. Israeli officials said Hamas, Gaza’s most powerful militant group, must be dealt a strong deterring blow before any ceasefire.

The UN Security Council will publicly discuss the worsening violence between Israel and Palestinian militants on Sunday, diplomats said after the United States earlier objected to a meeting on Friday.

The sound of artillery fire and explosions echoed across northern and eastern parts of Gaza into early Friday morning. Witnesses said many families living in areas near the border quit their homes, some seeking shelter at United Nations-run schools.

At least 109 people were killed in Gaza, including 29 children, over the previous four days, Palestinian medical officials said. On Thursday alone, 52 Palestinians were killed in the enclave, the highest single-day figure since Monday.

Seven people were killed in Israel: a soldier patrolling the Gaza border, five Israeli civilians, including two children, and an Indian worker, Israeli authorities said.