Israel's military has said it is investigating "harm caused to civilians" from an air strike it launched in Gaza.
Palestinian medics said eight members of one family died in the strike, among them five children.
Israel said the attack targeted the home of Rasmi Abu Malhous, who it called a militant commander from the group Palestinian Islamic Jihad (PIJ).
It said no civilians were expected to be in harm's way.
The attack in Deir al-Balah, in central Gaza, was the deadliest episode in a two-day exchange of fire between Israel and the Palestinian group.
It took place on Thursday, shortly before a fragile ceasefire came into effect.
Early on Saturday, Israeli air raids struck Hamas targets for the first time in the latest violence.
What happened in Thursday's incident?
The missiles hit an open sandy area, obliterating what neighbours and relatives described to the BBC as flimsy tin-roofed buildings inhabited by 22 people - the families of two brothers.
There were conflicting local accounts about whether one of them may have been linked to Islamic Jihad.
The Israeli military originally insisted that the head of the family, who it said was killed, was a commander of a PIJ rocket-launching unit.
Israel now says the information about his identity is not certain and is being reviewed.
Islamic Jihad did not comment on whether Abu Malhous was a member.
What is the latest on the fighting?
Israel says its air defences intercepted two rockets fired from Gaza at the southern Israeli city of Beersheva on Saturday.
In response, the Israeli Defense Forces said they struck "Hamas terror targets" in Gaza. Hamas' al-Aqsa TV reported a naval facility and a site in Beit Lahia being hit.
Up till now, Israel has avoided targeting Hamas, which controls the Palestinian territory.
For 1st time this week #Israel has struck #Hamas targets. Til now it's been narrowly targeting Islamic Jihad, trying to keep Hamas out of the fighting. But after rockets continue to violate Cfire, #Israel reverting to trad position that Hamas responsible for any #Gaza violence— Barbara Plett Usher (@BBCBarbaraPlett) November 16, 2019
What caused the current violence?
Fighting flared after Israel killed a PIJ commander in the early hours of Tuesday.
Israel said the commander, Baha Abu al-Ata, was a "ticking bomb" who was behind a planned imminent attack and responsible for recent rocket-fire from Gaza.
More than 450 rockets and mortars were fired at Israel, and several waves of air strikes carried out on Gaza in two days of violence.
The fighting left 34 Palestinians dead and 111 injured, while 63 Israelis needed medical treatment.
Israel said 25 of the Palestinians killed were militants, including those hit while preparing to launch rockets.