Turkey has deployed dozens of disaster relief specialists to help search for bodies under the mountains of rubble in Gaza, as US President Donald Trump fired a warning at Hamas over a spate of recent killings in the territory.

Trump characterised the killings as a breach of the ceasefire deal he spearheaded, under which the Palestinian militant group returned its last 20 surviving hostages to Israel.

Hamas says it has also handed back all the bodies of deceased captives it can access but the bodies of 19 more are still unaccounted for and believed to be buried under the ruins alongside an untold number of Palestinians.

The Palestinian militants stressed their "commitment" to the ceasefire deal with Israel, and that they want to return all the remaining bodies of hostages left in Gaza.

But it said in a statement that the process "may require some time, as some of these corpses were buried in tunnels destroyed by the occupation, while others remain under the rubble of buildings it bombed and demolished".

Turkey has sent staff from its disaster relief agency to help in locating the bodies but the families of the dead have fumed at Hamas's failure to deliver their loved ones' remains.

The main campaign group advocating for the hostages' families demanded on Thursday that Israel "immediately halt the implementation of any further stages of the agreement as long as Hamas continues to blatantly violate its obligations regarding the return of all hostages and the remains of the victims".

Israeli Prime Minister Benjamin Netanyahu reaffirmed his determination to "secure the return of all hostages" after his defence minister warned on Wednesday that Israel "will resume fighting" if Hamas failed to do so.

Trump had appeared to call for patience when it came to the bodies' return – insisting Hamas was "actually digging" for hostages' remains – but later expressed frustration on Thursday with the group's conduct since the fighting halted.

"If Hamas continues to kill people in Gaza, which was not the Deal, we will have no choice but to go in and kill them," Trump said on Truth Social in an apparent reference to recent shootings of Palestinian civilians.

Hamas has been accused of carrying out summary executions in Gaza since the ceasefire went into effect.

Clashes have also taken place between the group's various security units and armed Palestinian clans, some of which are alleged to have Israeli backing.

The ceasefire deal has so far seen the war grind to a halt after two years of agony for the hostages' families, and constant bombardment and hunger for Gazans.

According to Trump's 20-point plan for Gaza, the next phases of the truce should include the disarmament of Hamas, the offer of amnesty to Hamas leaders who decommission their weapons and establishing the governance of post-war Gaza.

The plan also calls for renewed aid provision, with international organisations awaiting the reopening of southern Gaza's Rafah crossing in the hope it will enable a surge of supplies.

Israeli Foreign Minister Gideon Saar said on the sidelines of a summit in Naples that preparations were being made for the strategic crossing, and that he "hoped" it would reopen on Sunday, Italian news agencies reported.

Israel, however, said earlier on Thursday that the crossing would only be open to people, not aid, and Saar did not appear to elaborate, according to the reports.

The humanitarian situation has been dire in Gaza throughout the war, with the UN declaring famine in parts of the north in August.

The World Health Organization has warned that infectious diseases are "spiralling out of control", with only 13 of the territory's 36 hospitals even partially functioning.

"Whether meningitis... diarrhoea, respiratory illnesses, we're talking about a mammoth amount of work," Hanan Balkhy, regional director for the UN health body, told AFP in Cairo. (AFP)