The Palestinian militant group Islamic Jihad says another of its top commanders has been killed in an Israeli airstrike. Israeli security forces say they have also arrested 20 members of the group in the West Bank.

The Palestinian Islamic Jihad militant group said on Sunday its top commander for the southern Gaza Strip, Khaled Mansour, was killed in an Israeli airstrike late on Saturday amid the worst cross-border conflict between Israel and Palestinian militants since last year.

The news comes as Israeli security forces said 20 members of the Islamist group have been arrested. Israeli officials claim the Islamic Jihad has been preparing an attack on Israeli-controlled territory in the West Bank.

Cross-border violence has flared since Israel killed the Iranian-backed group's commander for northern Gaza in an air raid on Friday.

IDF says they 'thwarted' terror attack

The Al-Quds Brigades of Islamic Jihad said Saturday's airstrike in the southern Gaza city of Rafah killed two fellow militants along with Mansour, as well as five civilians, including a child and three women.

The Israel Defense Forces (IDF) said in a statement that "in recent days Mansour worked to carry out an anti-tank missile and rocket attack at Israel and was responsible for the planning of a terror attack in Israel along the border with Gaza which was thwarted by the IDF."

The Health Ministry in Gaza said on Sunday that altogether 29 people, including six children, had been killed since Friday in Israeli strikes.

Israeli authorities, in their turn, have blamed the children's deaths on Saturday in the town of Jabaliya on a misfired rocket launched by Gaza militants toward Israel.

Israel estimates its airstrikes have killed about 15 militants.

Sirens sound in Jerusalem

Islamic Jihad militants have continued firing rockets at Israel overnight, while the Israeli military has kept up airstrikes on Gaza, but the intensity was reported to have diminished by Sunday morning.

However, air raid sirens sounded in the Jerusalem area on Sunday, the army said, as rocket fire continued from the Gaza Strip.

The Islamic Jihad group said its attack on the western outskirts of the city was in retaliation for the killing of Mansour. There was no immediate report of casualties.

The renewed violence has forced Gaza's only power plant to close for lack of fuel, aggravating the territory's power crisis at the peak of the summer.