Israel launched air strikes in the Gaza Strip on Monday after a rocket attack near Tel Aviv wounded seven people, prompting Prime Minister Benjamin Netanyahu to cut short a visit to the United States.
Netanyahu had threatened strong retaliation for the long-range rocket salvo amid accusations from opponents in a closely contested election, two weeks away, that he has been showing weakness in the face of security challenges from Gaza militants.
"The Israel Defence Forces have begun striking Hamas terror targets throughout the Gaza Strip," the military said in a statement.
Netanyahu, who arrived in Washington on Sunday for a four-day visit, said he would fly home right after meeting President Donald Trump at the White House on Monday.
The Israeli military said Hamas, a Palestinian militant group that rules Gaza, launched the rocket that destroyed a house in Mishmeret, a village north of Tel Aviv.
There was no claim of responsibility for the early morning attack. The military said Hamas fired the rocket from about 120 kilometres away, making it the longest-range attack from Gaza causing casualties since a 2014 war.
Palestinian security officials said Israeli warplanes attacked targets across the coastal enclave. Palestinian radio stations and Hamas TV played patriotic songs calling for "resistance" against Israel.
There were no immediate reports of casualties in the Gaza Strip. Many targets were likely to have been evacuated in the hours following Netanyahu's initial warning of retaliation shortly after the rocket strike.
Condemning the attack from Gaza, Trump told reporters with Netanyahu at his side that Israel has the "absolute right" to defend itself.
"Israel will not tolerate this. I will not tolerate this," Netanyahu said about the rocket strike.
"And as we speak ... Israel is responding forcefully to this wanton aggression."
Israel's Magen David Adom ambulance service said it treated seven people in the Israeli village, including an infant, a 3-year-old boy, a 12-year-old girl and a 60-year-old woman who was suffering from blast injuries, burns and shrapnel wounds.
"It just made me feel really unsafe all of a sudden, which is a feeling I'm not used to," said Nitzan Shifrin, a 19-year-old resident of Mishmeret.
The Israeli military said it was assigning two brigades to the Gaza area and some reservists were being called up.
Reuters witnesses saw troops moving towards the border, where the military also closed several roads to civilian traffic.
"We are prepared for a wide range of scenarios," chief spokesman Ronen Manelis said.
Israeli towns near Gaza and Tel Aviv, Israel's commercial capital, opened bomb shelters in anticipation of rocket strikes.
The rocket attack coincided with tension ahead of the March 30 anniversary of Gaza protests that have included Palestinian attempts to breach the frontier and often lethal Israeli fire.
Gaza authorities have said that some 200 people have been killed by Israeli fire in the protests. An Israeli soldier was killed by a sniper along the frontier.
The protesters demand the right to return to land from which their ancestors fled or were expelled in fighting that accompanied Israel's founding in 1948.
Israeli-Palestinian peace talks have been frozen since 2014.
The Gaza war that year was the third between Israel and Hamas in a decade. More than 2,100 Palestinians, most of them civilians according to the Gaza health ministry, were killed in seven weeks of fighting. Sixty-six Israeli soldiers and seven civilians in Israel were killed.
Some commentators in Israel drew a link between Monday's rocket fire and recent street protests in Gaza against higher prices, demonstrations which the United Nations said triggered a Hamas campaign of arrests and violence.
"Having failed to quell the protests with a violent crackdown, Hamas chose a new tack. What better way to distract their public, and turn their ire away from Hamas and back toward Israel, than to provoke a heavy Israeli response?" Dan Shapiro, a former US ambassador to Israel, wrote on Twitter.
Two rockets were fired at Tel Aviv on March 14 but caused no injuries or damage. Israel blamed them on Hamas, though a security official later said the salvo was set off by accident.
Palestinians in Gaza have also frequently launched incendiary balloons towards Israeli farms and villages along the frontier — attacks that have triggered Israeli air strikes, at times against Hamas facilities abandoned in advance.
Recent Gaza violence has dented Netanyahu's tough-on-security image at a time when he is running neck-and-neck with centrist challenger Benny Gantz, a former armed forces chief.
Netanyahu's visit to Washington, after Trump said it was time to recognise Israel's sovereignty over the Golan Heights, an area it captured from Syria in the 1967 Middle East war, was seen at home as a bid to boost the right-wing Likud leader's chances of a fifth term.
At their White House meeting, Trump signed a declaration codifying US recognition of Israel's hold on the strategic plateau, a dramatic shift from decades of US policy. Syria called the move "a blatant attack" on its sovereignty and territorial integrity.
Netanyahu's election prospects have been clouded by graft allegations against him. He has denied any wrongdoing.