The Israeli military said it had targeted commanders and sites belonging to Palestinian militant group Hamas and its ally Islamic Jihad in response to a breach of a US-brokered ceasefire agreed last October after two years of war in the Gaza Strip.
Hamas, which retains control of just under half of the enclave, said Israel had violated the truce.
It did not say whether any of its members or sites were struck in Saturday's attacks.
Israel carried out the attacks a day before the Rafah border crossing between the Gaza Strip and Egypt is due to reopen under US President Donald Trump's plan to end a war that has left much of the strip in ruins.
The war began after Hamas-led gunmen attacked southern Israel on October 7, 2023.
Israeli officials have said the war could resume if Hamas does not lay down its weapons.
Israeli warplanes bombed the Sheikh Radwan police station west of Gaza City, killing 10 officers and detainees, medics and police said.
Rescue teams were searching for more casualties at the site, the Hamas-run police said.
Other air strikes hit at least two houses in Gaza City, in northern-central Gaza, and a tent encampment sheltering displaced Palestinians in Khan Younis further south, local officials said.
Video footage from Gaza City showed charred, blackened and destroyed walls at an apartment in a multi-storey building, and debris scattered inside it and outside on the street.
"We found my three little nieces in the street. They say 'ceasefire' and all. What did those children do? What did we do?" said Samer al-Atbash, an uncle of the three dead children.
The Israeli military said that in addition to targeting Hamas commanders, it also hit weapon caches and manufacturing sites.
It said the strikes were carried out in response to an incident on Friday in which troops identified eight gunmen emerging from a tunnel in Rafah, an area in the south of the enclave where Israeli forces are deployed under the truce agreement.
Three of the gunmen were killed by the forces and a fourth, whom the Israeli military described as a Hamas commander in the area, was arrested.
Hamas did not comment on the incident.
Dozens of its fighters have been trapped in tunnels under Rafah since the ceasefire although some have since been killed in clashes with Israeli forces.
Violence has repeatedly shaken the ceasefire.
Israeli fire has killed more than 500 people, most of them civilians according to Gazan health officials, and Palestinian militants have killed four Israeli soldiers, according to Israeli authorities.
The two sides have traded blame over truce violations, even as US officials press them to proceed to the next phases of the ceasefire deal, which is meant to end the conflict for good.
The next phase of Trump's Gaza plan includes complex issues such as Hamas disarmament, which the group has long rejected, further Israeli withdrawal from the Gaza Strip and the deployment of an international peacekeeping force.
Reuters reported on Monday that Hamas is seeking to incorporate its 10,000 police officers into the new US-backed Palestinian administration, a demand likely to be opposed by Israel.
