JERUSALEM: Prime Minister Benjamin Netanyahu warned Tuesday that Israel would step up attacks on Gaza's Islamist rulers Hamas after two Israeli women were killed by rockets fired from the enclave.

"Since yesterday, the army has carried out hundreds of attacks against Hamas and Islamic Jihad in Gaza... and we will further intensify the power of our attacks," Netanyahu said in a video released by his office, adding that Hamas "will be hit in ways that it does not expect".

The Israeli leader was speaking after two Israeli women were killed in the southern city of Ashkelon by rockets fired from the Gaza Strip.

"We deplore the death of two Israeli women and I ask you to respect the security instructions," Netanyahu added, addressing Israelis at the end of a security meeting in southern Israel.

Hamas said it fired 137 rockets in five minutes on Tuesday afternoon at Ashkelon and nearby Ashdod, in simultaneous strikes aimed at thwarting Israel's air defences.

The Israeli army has stepped up air strikes on suspected Hamas and Islamic Jihad positions in Gaza, where health authorities say 26 people have been killed in the exchange of fire since Monday, including nine children.

"We have eliminated commanders, hit many important targets and we have decided to attack harder and increase the pace of attacks," Netanyahu said.