Hamas has recalled about 7,000 members of its security forces to reassert control over areas of Gaza recently vacated by Israeli troops, according to local sources.
The Palestinian group also appointed five new governors, all with military backgrounds, some of whom previously commanded brigades in Hamas's armed wing.
The mobilisation order was reportedly issued via phone calls and text messages which said the aim was to cleanse Gaza of outlaws and collaborators with Israel and told fighters to report within 24 hours.
Reports from Gaza suggest that armed Hamas units have already deployed across several districts, some wearing civilian clothes and others in the blue uniforms of the Gaza police.
Tensions rose sharply and quickly after two members of Hamas's elite forces were shot dead by gunmen from the powerful Dughmush clan in Gaza City's Sabra neighbourhood. One of them was the son of a senior commander in Hamas's armed wing, Imad Aqel, who now heads the group's military intelligence.
Their bodies were left in the street, triggering anger and raising the prospect of a major armed response by Hamas.
Hamas members later surrounded a large area where more than 300 Dughmush gunmen were believed to be holed up, armed with machine guns and improvised explosives.
This morning Hamas killed one Dughmush clan member, and reportedly kidnapped another 30.
Some of the clan's weapons were looted from Hamas depots during the war, while others had been in the clan's possession for years.
The Hamas mobilisation had been widely anticipated amid growing uncertainty about who will govern Gaza once the war ends.
This is a key issue that could complicate the start of the second phase of US President Donald Trump's peace plan, which calls for Hamas to disarm.
A Hamas official abroad declined to comment directly on reports of the security deployment but stated, We cannot leave Gaza at the mercy of thieves and militias backed by the Israeli occupation. Our weapons are legitimate... to resist occupation, and they will remain as long as the occupation continues.
A retired security officer who served for years with the Palestinian Authority in Gaza expressed concern that the territory was sliding towards another round of internal bloodshed, emphasizing the significant number of arms circulating within Gaza.
Khalil Abu Shammala, a human rights expert, noted widespread fear among Gazans of potential internal fighting, given the prevailing conditions.