Israeli air strikes hit four targets in Gaza overnight, wounding four people, three of them children, medical and security sources said on Thursday, as violence surged on the border.
It was the biggest flare-up in months and raised concerns for a ceasefire between Israel and Gaza's Hamas rulers that has held since the last round of major hostilities in the territory ended in summer 2014.
The Israeli army said that a major target of the strikes was suspected infiltration tunnels under the border like those whose destruction it cited as one of the principal achievements of the 2014 conflict.
It gave no word on casualties but medical sources in Gaza said a raid on the Al-Zeitoun district wounded four members of the same family -- three children and a 65-year-old man.
The raid hit a garage, its owner Hasan Hasaneen told AFP, saying the vehicles that caught fire were not used by security forces but only for "reconstruction works."
Gaza has been devastated by three conflicts between Israel and its Hamas rulers and other Palestinian factions since 2008, and reconstruction has been painstakingly slow amid an Israeli blockade on all imports that could have military purposes.
Hamas-run interior ministry said two raids targeted a base of the military wing of Islamic Jihad, causing damage but no casualties.
Over the past two days, Israeli soldiers operating along the fence that tightly encloses the territory have been repeatedly targeted from inside Gaza, the army said.
On Wednesday, the army said it hit five Hamas-run sites in the south of the territory in response to mortar fire across the border.
Those strikes hit around Gaza's derelict international airport near the southern city of Rafah and in nearby farmland, the Hamas-run interior ministry said.
The army also established a closed military zone around the small Israeli border town of Nahal Oz, saying troops had been fired on in the area.
- 'One fuse too many' -
There was no claim of responsibility for the mortar fire that hit Israel.
But both Hamas and Islamic Jihad released statements warning Israel against any escalation.
Hamas's armed wing, the Ezzedine al-Qassam Brigades, said it was ready to respond to Israeli strikes.
"We will not permit this aggression to continue and the enemy should not invoke any reason and leave the Strip immediately," the group said.
The border region has remained relatively quiet since the 2014 conflict, despite allegations by the army that Hamas is building new tunnels from the enclave that could reach into Israel.
Israel cited the destruction of such tunnels as a major achievement of the 50-day conflict in 2014, which killed 2,251 Palestinians, mostly civilians, and 73 Israelis, including 67 soldiers, according to the United Nations.
The UN special coordinator for the Middle East peace process, Nickolay Mladenov, said on Wednesday he was "concerned" about the flare-up on the Gaza border.
"It is critical that peace be maintained to ensure the safety and security of Israelis and Palestinians alike," he said.