Israel’s military said Saturday that it has struck two Hamas targets in the Gaza Strip in response to rocket fire toward the Jewish state, as the worst flare-up of violence since the 2014 war entered a fourth day.

The military said sirens wailed in southern Israel early Saturday warning of an incoming rocket. One landed in an open field, causing no injuries.

The statement said the army retaliated against the territory’s Hamas rulers by striking two of the group’s “infrastructures.”

Gaza militants have fired mortar rounds at Israel over the past three days, prompting Israeli retaliation.

Palestinian attacks intensified after Israel uncovered an attack tunnel Thursday beneath the border.

Hamas used tunnels to attack Israel during the 50-day Gaza war in 2014 and fired thousands of rockets.

The recent exchanges of fire are among the most serious since the end of the war which left 2,251 Palestinians and 73 Israelis dead in 2014.

The leader of Hamas in Gaza said on Friday the group was “not calling for war” with Israel, and that Egypt and other parties were working behind the scenes to defuse the violence.

“We are not calling for war but we will not allow incursions at all,” said Ismail Haniyeh, Hamas’s deputy chief, speaking at a mosque before Friday prayers.

“The resistance will not allow the establishment of a so-called buffer zone inside the borders of the Gaza Strip.”