Medics said that one strike on a house in Bani Suhaila town east of Khan Younis killed three people, including a baby girl, and wounded 15 others while another killed a man and wounded three others in the nearby Abassan town.
Israel's military confirmed the strikes but said it was not aware of casualties.
Later on Thursday, Nasser Hospital officials said a fifth Palestinian was killed by Israeli gunfire in Abassan town too.
On Wednesday, Israel said it struck targets across the enclave after members of the Palestinian militant group fired on its troops, and Gazan medics said at least 25 people were killed, the highest toll since October 29, when at least 100 people were killed.
Hamas called the attacks a dangerous escalation and urged Arab mediators, Turkey and the United States, which brokered the ceasefire, to intervene.
In a statement later on Thursday, Hamas spokesman accused Israel of changing markings that define areas Israel still occupies, in violation of the agreed-upon maps, which keeps Israel in control of over 50 per cent of the enclave's areas.
Residents told Reuters they saw that in Shejaia suburb in eastern Gaza City, adding that yellow barricades marking areas still under Israel's control had been moved 100 metres westward.
There was no immediate Israeli comment on the positioning of the markings.
In Gaza City's Zeitoun suburb, where at least 10 people were killed in a building that used to house displaced families on Wednesday, Palestinians sifted through the wreckage to salvage furniture and belongings as rescue workers searched for any further victims.
"They say there is a ceasefire but I doubt this. Day by day, they say there is a ceasefire, this is completely untrue," Zeitoun resident Akram Iswair said on Thursday.
"Missiles struck the displaced, poor citizens. What can we, our women and our families do?" he told Reuters.
The October 10 ceasefire in the two-year Gaza Strip war has eased the conflict, enabling hundreds of thousands of Palestinians to return to the enclave's ruins.
Israel has pulled troops back from city positions, and aid flows have increased.
Meanwhile, more than 60 delegations met in Brussels on Thursday to discuss reconstruction, governance and security in the Gaza Strip and reforming the Palestinian Authority.
France and Saudi Arabia chaired a meeting of the Palestine Donor Group, focusing on reforms of the Palestinian Authority (PA) called for by a US peace plan that won approval at the United Nations Security Council on Monday.
The Palestinian Authority administers semi-autonomous pockets in the Israeli-occupied West Bank and is making a renewed push to become a player in the postwar Gaza Strip.
The European Union, the Palestinian Authority's largest financial supporter, hopes the PA can effectively rule the Gaza Strip after deep reforms.
But US officials want the Palestinian Authority to make reforms first, and Israel rejects any role for it in the Gaza Strip.
The EU is planning to train 3000 Palestinian police officers to secure the Gaza Strip.
French Foreign Minister Jean-Noël Barrot pledged 100 French police officers for that mission.
The EU hopes to recruit from a pool of about 7000 Gazan police officers once paid by the Palestinian Authority, said a senior official tasked with communicating for the EU foreign policy service but not authorised to be publicly named.
The EU is discussing with "neighbouring countries" of the Gaza Strip to host the training program.
with AP
