"We have struck 130 military targets belonging mostly to Hamas," the Islamist group that controls the blockaded Gaza strip, Israeli army spokesman Jonathan Conricus told reporters.

"According to our current estimates we have killed 15 Hamas and Islamic Jihad operatives," he said.

Violence has spiralled since clashes with Israeli police in the flashpoint Al-Aqsa mosque compound wounded hundreds of Palestinians.

The clashes started after Palestinians hurled projectiles at Israeli security forces.

Hamas gave Israeli forces a 1500 GMT Monday deadline to vacate Al-Aqsa, Islam's third holiest site.

Shortly after the deadline expired, Hamas and other armed groups in the Israeli-blockaded Gaza strip unleashed a barrage of rockets towards Israel, including Jerusalem.

Conricus said more than 200 rockets had been fired from Gaza since Monday, with more than 90 percent of those intercepted by Israel's Iron Dome defence system.

Health authorities in Gaza have put the death toll from the air strikes strikes at 22, including nine children.

Conricus said Israel could not yet confirm or deny that its strikes caused civilian casualties in the strip.

He said Hamas was trying to "nurture a narrative of damage to non-combatants done by Israel. That is not true."

Israel's army estimated that roughly a third of the rockets launched by militants had "fallen short," landing inside Gaza, and may be responsible for Palestinian casualties, Conricus said.

He told reporters that sites targeted so far included weapons manufacturing and storage facilities, training sites and military bases in Gaza.

The home of one militant commander and a "Hamas intelligence centre" were also targeted, the spokesman said, without providing details.

"We are in the early stages of our counter strikes... They will continue."