Hamas militants in Gaza fired "dozens" of rockets into southern Israel late Monday, the Islamist movement said after six of its men died as tensions soared around the Palestinian enclave.
The bombardment was confirmed by the Israeli army which said militants had launched "a few dozen rockets" within a short period of time.
At least four were intercepted over Netivot by the Iron Dome anti-missile system, while another 16 struck the area around the southern city of Beersheva, some 40 kilometres (25 miles) from Gaza, and which is home to 200,000 people, the army said.
Media reports put the number of rockets at around 40, but there were no immediate reports of casualties.
Sirens sounded in several locations south of Tel Aviv, public radio said.
The rocket fire was claimed by Hamas's armed wing, the Ezzedine al-Qassam Brigades, in a statement sent to AFP in Gaza.
"Al-Qassam fired dozens of rockets on Netivot and Ashkelon, Ashdod and Ofakim in response to the Zionist aggression," a statement said.
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Shortly afterwards, the Israeli air force hit more than 30 targets near southern city of Rafah in an area close to the Israeli border which is riddled with tunnels, Palestinian witnesses and security sources told AFP.
Israel's Channel 1 television said the attacks came after the security cabinet gave the military a green light to "toughen the response to Hamas."
The channel also showed footage of dozens of tanks massing near the border with Gaza, preparing for a possible offensive against the enclave.
"With this barrage of rockets, Hamas has crossed the red line and unfortunately, it will pay for it," senior officials told Israel's Channel 10 television.
The rocket fire came several hours after Israel staged around 16 air strikes on targets across Gaza, following a night in which warplanes had attacked 14 targets, killing at least three militants.
Another five Hamas militants died and one was left in critical condition when a tunnel collapsed near the southern city of Rafah, with the movement blaming it on an Israeli air strike.
But the Israeli army denied hitting the area where the tunnel was, with a spokesman describing it as a work accident by militants handling explosives.
There was no immediate word on casualties or damage in Israel from the latest rocket attacks.