GAZA/JERUSALEM - Israel rushed an eighth missile interceptor battery into service on Saturday to counter stronger-than-expected rocket fire from Gaza as the military pounded positions in the Palestinian enclave for a fifth day, killing 19 people, medics said.

The Jewish state kept options open for a possible ground offensive into densely populated Gaza despite international pressure to negotiate a ceasefire in the conflict, which has killed 125 people in the Islamist-ruled enclave since Tuesday.

The UN Security Council, after days of discussion, issued a statement calling for a ceasefire and expressed serious concern about the welfare of civilians on both sides.

"The Security Council members called for de-escalation of the situation, restoration of calm and reinstitution of the November 2012 ceasefire," the 15-member body said.

A mosque in the central Gaza Strip had been bombed to rubble, residents said. The Israeli military said the mosque had housed a weapons cache. Eight other mosques have been damaged by bombing and 537 Gaza houses have either been destroyed or damaged, Gaza-based Al-Mezan Association for Human Rights said.

By Saturday, no Israeli had been killed by the rocket salvoes out of Gaza, due in part to Iron Dome, a partly US-funded interceptor system.

Racing for shelter has become a daily routine for hundreds of thousands of Israelis, and some 20,000 reservists have been mobilised for a possible thrust into Gaza.

"In the past week, we carried out a very complex technological exercise to deliver the eighth (Iron Dome) system," a Defence Ministry official said on Israel Radio.

Israel said it was determined to end cross-border rocket attacks, which intensified last month after its forces arrested hundreds of activists from the Islamist Hamas movement in the West Bank after the abduction there of three Jewish teenagers who were later found killed. A Palestinian youth was then killed in Jerusalem in a suspected revenge attack by Israelis.