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STORY: Video from Gaza released early in December shows the new leader of a Palestinian militant group opposed to Hamas reviewing armed fighters under his command.
The group, known as the Popular Forces, is among those that have emerged in Israel-held parts of Gaza, eyeing a role in the enclave's future.
They are small, but have added pressure on Hamas and could complicate efforts to unify and stabilize a divided Gaza shattered by two years of brutal war.
Three Egyptian security and military sources said Israel-backed groups were increasingly active since a cease-fire took effect, and estimated they now had 1,000 fighters, adding 400 since the truce began.
But they have faced setbacks.
Just last week, the man seen at the heart of efforts to establish anti-Hamas forces - Popular Forces leader Yasser Abu Shabab - was killed.
The Popular Forces did not say who killed him. His deputy, Ghassan Duhine, has taken over and vowed to continue on the same path.
Recent footage showed Duhine alongside Hussam Alastal, leader of another group, pledging to jointly continue the fight against Hamas.
Hamas has branded such groups collaborators.
A Hamas spokesperson, Hazem Qassem, said security forces would pursue collaborators "until this phenomenon is eradicated."
But they "are protected by the occupation army in the areas where these forces are present, which makes it difficult for the security apparatuses," he said, speaking to Reuters before Abu Shabab's death.
Hamas moved swiftly against Palestinians who defied its control after the U.S.-backed ceasefire took hold, killing dozens, including some it accused of working with Israel.
The Popular Forces didn't respond to requests for comment sent via their Facebook page. It has previously denied receiving Israeli support.
In an interview with Reuters in late November, Alastal said fortunes for groups such as his were improving.
Despite Hamas accusations of collaborating with Israel, Alastal said his group was not a militia, but an administration. He said the group was present for the people, to build a new Gaza.
Nearly all Gaza's 2 million people live in Hamas-held areas. The group is reestablishing its grip and four Hamas sources said it still commands thousands of men.
But Israel still holds over half of Gaza - areas where Hamas' foes operate beyond its reach. With U.S. President Donald Trump's plan for Gaza moving slowly, there is no immediate prospect of further Israeli withdrawals.
Israeli Prime Minister Benjamin Netanyahu acknowledged in June that Israel had armed anti-Hamas clans, though Israel has given little detail since then.
In response to a request for comment, an Israeli government official said: "There is no shortage of Palestinians wishing and actively fighting to free themselves of the Hamas repression and tyranny."
Israel has established what it calls the "Yellow Line," a defensive border separating Israeli-controlled areas from Hamas-held territory.
With no clarity on next steps, there is a risk of de facto partition between an inland sector controlled by Israel where few people now remain, and a sector along the coast now crowded with displaced people, much of it wasteland.
On a tour of Israeli military positions in Gaza, an army spokesperson said for now they were just keeping Hamas penned in.
"We are holding the yellow line that is the current border. And what happens next depends on the situation on the ground. Right now, Hamas is refusing to disarm. Hamas is the main blocking point of this plan moving forward. And we are currently holding the yellow line, according to the agreement, making sure Hamas doesn't cross it or violate it."
Many of the armed anti-Hamas groups operate in Israel-held areas, a fact that a Hamas spokesperson said effectively made them a part of what they called the "occupation army."
That impression may limit their role in governing Gaza.
"I don't think there is any serious future for these new groups that are associated with the Israeli occupation in Gaza."
Ghassan al-Khatib is a lecturer in international studies at Birzeit University in Ramallah.
"The reason is that the public is not at all accepting them. They are not acceptable by the public because of the cooperation and collaboration with the Israeli occupation."
Al-Khatib noted Israel had plenty of experience propping up Palestinian armed groups for short-term tactical reasons.
A U.S. official said Washington has not had any official contact with the anti-Hamas groups. They added, "Beyond Hamas having no future role, who will govern Gaza will be up to Gazans."
