Tensions remain high after a night of heavy weapons fire between the Gaza Strip and Israel.
Dozens of rockets fired from Gaza lit up the sky, following the killing of at least 10 people in Israeli air strikes.
Militant leader Tayseer Jabari was among the dead. Israel said the strikes followed an "immediate threat" from his Palestinian Islamic Jihad (PIJ) group.
A five-year-old girl in Gaza also died, local health officials said, and dozens more were injured.
PIJ responded by firing more than 100 rockets into Israel overnight "in an initial response".
Most were intercepted by Israel's Iron Dome missile defence shield, but sirens sounded in a number of Israeli cities throughout the night.
The Israel Defense Forces (IDF) said it had resumed rocket strikes against multiple militant positions in Gaza, continuing the attacks into the early hours of the morning.
On Saturday, Israel said it had arrested 19 members of PIJ in raids across the West Bank.
The overnight exchange of fire marks the most serious escalation in violence since May 2021's 11-day war, which left more than 200 Palestinians and a dozen Israelis dead before a ceasefire was agreed.
Egypt, which has acted as a mediator between the two sides in the past, is reportedly offering to act as a go-between once again in a bid to prevent further escalation.
Cairo officials were preparing on Saturday to host a potential delegation of PIJ representatives as part of that process, Egyptian media said.
Referring to the initial strike on Friday, Israeli Prime Minister Yair Lapid said: "Israel carried out a precise counter-terror operation against an immediate threat."
Meanwhile, Interior Minister Ayelet Shaked said: "We don't know how this will play out... but this could take time... this could be a lengthy round [of conflict] and a hard one."
The IDF said its attacks targeted sites linked to PIJ, including the high-rise Palestine Tower in Gaza City which was hit on Friday in a loud explosion which left smoke pouring from the building.
An Israeli military spokesman estimated "about 15 militants" were killed in the operation.
Local health officials inside Gaza say four PIJ militants, including Tayseer Jabari, have been killed since the strikes started.
The IDF said Tayseer Jabari was a "senior commander" in PIJ, and accused him of having committed "multiple terrorist attacks" against Israeli civilians.
Five-year-old Alaa Kaddum was among those killed in the strikes, local officials also said.
Gaza authorities said another 79 people were also injured, AFP news agency reports.
In remarks delivered while on a trip to the Iranian capital Tehran, PIJ secretary general Ziyad al-Nakhala said: "We will respond forcefully to this aggression, and there will be a fight in which our people will win."
"There are no red lines for this battle... and Tel Aviv will be under the rockets of the resistance".
Hamas, which governs the Gaza Strip, said the armed groups were "united" in battle and would not keep silent.
The latest conflict closely follows Israel's arrest of Bassem Saadi, reported to be the head of PIJ in the West Bank, on Monday night.
He was held in the Jenin area as part of an ongoing series of arrest operations after a wave of attacks by Israeli Arabs and Palestinians that left 17 Israelis and two Ukrainians dead. Two of the attackers came from the Jenin district.
After Bassem Saadi's arrest, Israel warned that PIJ intended to attack civilians and soldiers in retaliation - and so heightened security measures for communities living near the border with Gaza.
PIJ, which is one of the strongest militant groups operating in Gaza, is backed by Iran and has its headquarters in the Syrian capital Damascus.
It has been responsible for many attacks, including rocket-fire and shootings against Israel.
In November 2019, Israel and PIJ fought a five-day conflict following the killing by Israel of a PIJ commander who Israel said had been planning an imminent attack. The violence left 34 Palestinians dead and 111 injured, while 63 Israelis needed medical treatment.
Israel said 25 of the Palestinians killed were militants, including those hits preparing to launch rockets.
BDST: 1413 HRS, Aug 06, 2022