Israeli warplanes have attacked 29 Palestinian targets in the Gaza Strip in response to an Islamic Jihad rocket barrage into Israel earlier on Wednesday, the military has said.
Palestinian eyewitnesses and journalists said that warplanes hit bases of the Hamas rulers and the armed wing of Islamic Jihad.
Israel is also reported to have closed border crossings with the Gaza Strip.
Militants fired more than 30 rockets into southern Israel, officials say.
An Israeli military spokesman said five hit populated urban civilian areas.
He said that a number of others were intercepted by the Iron Dome missile defence system.
It was the heaviest barrage since the November 2012 conflict in Gaza ended.
Islamic Jihad said it fired the rockets in retaliation for Tuesday’s killing of three of its militants in an earlier Israeli air strike.
The Voice of Israel said on Wednesday that the Israeli Defence Force (IDF) had closed border crossings in response to the rocket attacks.
It cited Israeli Defence Minister Moshe Yaalon as saying that Israel held Hamas responsible for the escalation in violence and warned it would “pay a heavy price”.
But Hamas released an equally belligerent statement.
“Our mujahideen responded to the Zionist aggression by firing tens of rockets,” it said.
Speaking to the BBC, the group’s spokesman added: “The rockets fired today came in response to the occupation aggression against us and does not mean the collapse of the ceasefire agreement [with Israel].”
Another Gaza militant group, the Popular Resistance Committees, said it also fired several rockets.
An Israeli army statement late on Wednesday said that the remains of 60 rockets had so far been found.
Witnesses said that there were Israeli retaliatory strikes throughout the coastal strip on facilities operated by Islamic Jihad’s military wing, the al-Quds Brigades, and on targets belonging to Hamas’s military wing.
“In response to the massive rocket attack that hit Israel earlier this evening, the Israel Air Force targeted 29 terror sites in the Gaza Strip. Direct hits were confirmed,” the army statement said.
“This retaliation was precise and prompt. We targeted the infrastructure that serves the terrorists while they train, plan and implement their hideous attacks,” Lt Col Peter Lerner, the chief military spokesman, said in the statement.
“Code red” sirens had sounded across southern Israel after the militants had fired rockets.
One exploded near a petrol station and another near a public library, a police spokesman said.
A statement by the al-Quds Brigades said the barrage was its “initial response” to the “crimes of the Zionist enemy in the occupied West Bank and Gaza Strip”, the latest of which was the “assassination” of three of its members on Tuesday.
After Wednesday’s rocket barrage, Israeli Prime Minister Benjamin Netanyahu said: “We won’t flinch. We will continue to hurt those who try to hurt us.”
He said that the number of rockets this year has been the lowest in the past decade.
Iranian-backed Islamic Jihad and other groups have sporadically fired rockets and mortars at Israel since the 2012 conflict ended, while the Hamas movement that governs Gaza has refrained from doing so.
However, an Israeli military statement said it held Hamas “responsible for all attacks emanating” from the coastal territory.
Israel pulled its troops and settlers out of the Gaza Strip, now run by Hamas, in 2005. But it maintains a naval and air blockade and restricts the overland movement of people and goods across their shared border.