The Israeli military has carried out a number of strikes against Palestinian positions overnight in the Gaza Strip.
They came in response to a bomb attack on Saturday which wounded four Israeli soldiers.
Two Palestinians were killed by Israeli tank fire in Gaza. The Israeli air force also claimed to have destroyed a number of sites linked to Hamas.
It is one of the most serious escalations in violence since Israel and Hamas fought a war in 2014.
The Israeli army said it hit 18 Hamas military targets from Saturday night through to Sunday, including “weapons manufacturing infrastructure” and a tunnel being dug by militants.
It also targeted two observation posts.
Palestinian officials said three Hamas training camps and one belonging to a smaller group had been struck.
Hamas’s military wing, the Izzedine al-Qassam Brigades, claimed that it had used anti-aircraft missiles against Israeli jets flying over the coastal territory.
On Saturday two Palestinian teenagers were also killed by Israeli tank fire east of Rafah.
The pair were in a group approaching the border in “a suspicious manner”, Israel’s army said.
It came after four Israel Defense Forces (IDF) soldiers were injured, two seriously, in an explosion on Saturday afternoon east of the town of Khan Younis.
The army said the explosive device had been planted during a demonstration there on Friday and was attached to a flag which the troops attempted to remove.
Israeli Prime Minister Benjamin Netanyahu, who is attending a security conference in Munich, Germany, said: “The incident on the Gaza border is very serious. We will respond appropriately.”
Israeli media also said a rocket from Gaza fell near a house in the south of the country on Saturday evening. There were no casualties.
Israel holds Hamas responsible for all rocket and mortar fire from the territory. Hamas has fought three wars with Israel since 2008.
Correspondents say the border area has been generally quiet in the last few years but there has been an increase in violence since US President Donald Trump’s announcement in December recognising Jerusalem as Israel’s capital.
Israel regards Jerusalem as its indivisible capital. Palestinians want the east of the city, which Israel occupied in the 1967 Middle East war, to be a capital of a future state.
Israel Gaza: Air strikes follow bomb blast on Gaza border}