Israel said on Friday that it had struck more rocket-launching sites operated by the Palestinian Islamic Jihad militant group, in Gaza, and the group fired rockets into Israel, reaching as far as the hills around Jerusalem, as cross-border fighting stretched into a fourth day despite overnight mediation efforts to reach a ceasefire.

Israel has killed five Islamic Jihad commanders since the hostilities erupted on Tuesday, and the militant group has responded to Israeli attacks by firing more than 850 rockets and mortar rounds into Israel from Gaza, the Israeli military said.

At least 31 Palestinians have been killed, six of them children, the Palestinian Ministry of Health said on Friday. It said that more than 90 Palestinians had also been injured.

A rocket fired from Gaza on Thursday evening struck a residential building in Rehovot, a city in central Israel. One person was killed in that attack — the first casualty on the Israeli side in the several days of fighting.

Five more people were injured in that rocket attack, according to Israel’s ambulance service.

Israel has said that the Islamic Jihad commanders it targeted were responsible for firing rockets into Israel, including more than 100 projectiles that the group fired towards Israel on May 2.