Israeli planes hit Gaza in response to rocket strikes
Israeli warplanes have struck 29 targets in the Gaza Strip in response to a rocket barrage from Gaza into Israel, the military has said.
Palestinians said missiles hit bases of Gaza's Hamas rulers and the armed wing of Islamic Jihad, which had fired the rockets. Four more rockets were fired at Israel on Thursday, Israel said.
There are no reports of casualties on either side.
Militants fired some 60 rockets into Israel since Wednesday, officials say.
An Israeli military spokesman said eight hit populated urban civilian areas. The military said several rockets had been intercepted by the Iron Dome missile defence system.
It was the heaviest barrage since the November 2012 conflict between Israel and 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.
Israeli Defence Minister Moshe Yaalon said border crossings with Gaza would be closed "until further security assessments". He said Israel held Hamas responsible for the escalation in violence and warned it would "pay a heavy price".
Hamas and Islamic Jihad accused Israel of provoking the attacks.
"Our mujahedeen responded to the Zionist aggression by firing tens of rockets," Islamic Jihad said in a statement to the BBC.
"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]," it said.
Another Gaza militant group, the Popular Resistance Committees, said it also fired several rockets.
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.
Israeli army spokesman Lt Col Peter Lerner said the military had "targeted the infrastructure that serves the terrorists while they train, plan and implement their hideous attacks".
"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.
Correction 13 March 2014: An earlier version of this story wrongly attributed to Hamas a statement by Islamic Jihad.