Israel carried out its heaviest airstrikes in Gaza in weeks on Saturday, killing 26 people according to local health authorities, in attacks on a Hamas-run police station and on apartments and tents in an area sheltering displaced Palestinians.

Despite the tenuous ceasefire agreed between Israel and Palestinian militant group Hamas, Israeli warplanes targeted 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, said the police, who are run by Hamas in the Gaza Strip.

Another airstrike hit an apartment in Gaza City killing three children and two women, according to officials at Shifa hospital in the city. Seven more were killed in a strike at a tent encampment in Khan Younis further south.

An Israeli military source 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 southern Gaza where Israeli forces are presently deployed under the October ceasefire agreement.

Three of the gunmen were killed by the forces and a fourth, whom the Israeli military described as a key Hamas commander in the area, was arrested.

Hamas did not comment on the incident, which the military source said constituted a violation of the ceasefire, and it blamed Israel for breaching the truce.

Ceasefire steps ahead as sides trade blame for violations

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.

Israeli fire has killed more than 500 people, most of them civilians according to Gaza health officials, since the US-brokered truce between Palestinian militant group Hamas and Israel took effect in October after two years of war.

Palestinian militants have killed four Israeli soldiers since the truce, according to Israeli authorities.

The two sides have traded blame over truce violations, even as Washington presses them to proceed to the next phases of the ceasefire deal meant to end the conflict for good.

The next phase of US President Donald Trump's plan includes complex issues such as Hamas disarmament, which the group has long rejected, further Israeli withdrawal from Gaza and the deployment of an international peacekeeping force.

Gaza's main gateway, the Rafah border crossing with Egypt that has been largely shut during the war, is expected to reopen on Sunday.