Islamic Jihad vowed to "avenge" the deaths in the pre-dawn raid involving some 40 Israeli aircraft, which hit targets in the crowded coastal territory for nearly two hours from just after 2:00 am (2300 GMT Monday).

The Gaza health ministry said four children were among those killed and 20 people were wounded, some of them in serious or critical condition, in the attacks which left buildings ablaze and reduced others to rubble.

The Israeli army said that in its Gaza strikes it had targeted three leaders of Islamic Jihad, which it considers a terrorist group, as well as its "weapon manufacturing sites".

Asked about child casualties, army spokesman Richard Hecht said: "If there were some tragic deaths, we'll look into it."

Islamic Jihad confirmed three of its senior members were killed in Gaza.

It named them as Jihad Ghannam, secretary of the Al-Quds Brigades military council, Khalil al-Bahtini, commander of the military wing in northern Gaza, and Tareq Ezzedine, a military leader in the West Bank who operated from Gaza.

Mourners carried the bodies of those killed through the streets as funeral processions got underway.

Moscow's diplomatic mission to the Palestinians said one of the dead was a Russian citizen and doctor, who was killed alongside his wife and one of his children.

Islamic Jihad vowed to retaliate, with spokesman Daoud Shehab warning that "the resistance considers that all cities and settlements in the Zionist (Israeli) depths will be under its fire".

The Israeli military warned residents within 40 kilometres (25 miles) of the Gaza border to stay near bomb shelters until Wednesday evening.

Describing the air strikes as a "precise operation", Defence Minister Yoav Gallant said Israel "will not tolerate rocket fire, terrorism or any threats to the sovereignty of our state and security of our citizens."

- 'Avenge the leaders' -

Israel last week traded air strikes on Gaza for rocket fire from the enclave, an exchange sparked by the death in Israeli custody of a Palestinian hunger striker with ties to Islamic Jihad, which ended with an Egypt-brokered truce.

Islamic Jihad charged on Tuesday that Israel had "scorned all the initiatives of mediators" and vowed it would "avenge the leaders" killed in the latest air strikes.

"It's about time!" Israel's far-right National Security Minister Itamar Ben-Gvir wrote on Facebook, after criticising what he perceived as the military's weak response to Gaza militants last week.

The Israeli military described Ghannan as "one of the most senior members" of Islamic Jihad who had coordinated weapons and money transfers with Hamas.

Bahtini was "responsible for the rocket fire toward Israel in the past month", Israel said.

And Ezzedine, who was released from Israeli detention in a 2011 prisoner exchange, had been planning "multiple attacks against Israeli" civilians in the West Bank, it charged.

An Islamic Jihad source told AFP that Ezzedine was part of a delegation from the group that had been due to travel to Cairo for a meeting Thursday, which has now been cancelled.

- 'Treacherous operation' -

Hamas chief Ismail Haniyeh said in a statement that "assassinating the leadership in a treacherous operation will not bring security to the occupier, but instead greater resistance".

The United Nations' Middle East peace envoy, Tor Wennesland, said he was "deeply alarmed" by the latest violence and described the killing of civilians as "unacceptable".

Jordan's foreign ministry spokesman, Sinan Majali, said Amman was taking steps to "immediately stop this dangerous escalation."

Israel and Gaza militants have fought multiple wars since Hamas took control of the enclave in 2007.

A three-day conflict in Gaza last August left 49 Palestinians and no Israelis dead, with Cairo playing a key role in securing a ceasefire.

Following Tuesday's air strikes, Egypt's foreign ministry stated its "total rejection of such attacks".

Such actions "inflame the situation in a way that could get out of control in the occupied Palestinian territories."

The Gaza deaths bring to 121 the number of Palestinians killed in the Israeli-Palestinian conflict so far this year.

Nineteen Israelis, one Ukrainian and one Italian have been killed over the same period, according to an AFP count based on official sources from the two sides.