As Israeli forces retreated from Gaza last week, Hamas swiftly moved in to fill the void. This shift was marked by a surge in violence, including at least one public execution and skirmishes with competing factions, as the militant group sought to reestablish its dominance amidst the ceasefire in the devastated area.

Their message was unmistakable: Their presence remains strong.

According to experts, the demilitarization of Hamas is the most pivotal and challenging element of President Donald Trump’s peace initiative to put into practice.

The region of Gaza is a complex tapestry of various clans and militant groups, where vendettas and lawlessness continue to jeopardize stability in the Palestinian enclave, even after a ceasefire has been declared.

This week, Reuters acquired video footage purportedly showing masked gunmen executing several men on a street in Gaza City. The disturbing clip depicted at least six individuals being forced to their knees, their shirts pulled over their heads, before being shot.

Further video evidence revealed that at least two of the gunmen appeared to wear the green headbands synonymous with Hamas’ military faction, the Qassam Brigades. NBC News confirmed the video’s location within Gaza, although they could not verify the identities of the men as Hamas members.

Hamas did not immediately respond to a request for comment on the incidents. Last month, before the current ceasefire, Hamas-led authorities said three men were executed after being accused of collaborating with Israel, Reuters reported at the time.

President Donald Trump issued a clear warning about the violence on Thursday.

“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. Thank you for your attention to this matter!” he posted on Truth Social.

Asked at a press gathering whether he meant that U.S. troops could be involved, Trump said, “It’s not gonna be us. We won’t have to. There are people very close, very nearby that will go in. They’ll do the trick very easily but under our auspices.”

In the wake of Israeli troops’ initial withdrawal from parts of Gaza, Hamas, which has ruled over the enclave since 2007, has tried to regain control, with the militant group’s internal security organization issuing a call urging residents to report “wanted individuals,” including “collaborators” with Israel.

Israeli Prime Minister Benjamin Netanyahu had confirmed earlier this year that Israel had “activated” clans that oppose Hamas, which is designated a terrorist organization by the United States. His comments came after Israeli media, including the Times of Israel, reported he had authorized giving weapons to a particular group in southern Gaza, citing defense sources.

Calling on Hamas to “suspend violence” in the enclave on Wednesday, CENTCOM’s commander, m. Brad Cooper, said the truce brought by Trump’s 20-point ceasefire plan marked a “historic opportunity for peace.”

“Hamas should seize it by fully standing down,” he said.

Trump’s warning on Thursday followed comments earlier in the week in which he appeared to downplay the violence in Gaza, saying Hamas had taken out “a couple of gangs that were very bad,” before adding, “that didn’t bother me much.”

The flashes of violence this week came as the U.S. and Israel continued to call for Hamas’ disarmament, a key stipulation of Trump’s plan and a longstanding sticking point in talks for a lasting truce.

The Israeli military was accused of repeatedly opening fire on Palestinians this week amid the truce. The Israel Defense Forces acknowledged one incident Tuesday in which it said troops opened fire on people who came near forces stationed along the withdrawal line agreed under the first phase of Trump’s plan, which it said was a violation of the agreement.

Michael Wahid Hanna, the U.S. program director at the International Crisis Group, a global nonprofit based in Brussels, said there was still a lack of clarity around how the disarmament of Hamas might actually play out.

“None of this has been spelled out — what kind of weapons, under what conditions … none of it. None of it is on paper,” he said. “It is a kind of aspirational endpoint without many signposts about how to get there.”

What is clear, Hanna said in an interview on Wednesday, is that “Hamas is not gone.”

“I mean, lots of people have said this for a long time, that Israel would not be able to eliminate or destroy Hamas, and they haven’t,” Hanna said.

“They’ve probably eliminated Hamas as an actual threat to Israeli security, but in terms of Hamas in the Strip, they are still there and seemingly exercising some coherent control,” he said, noting that some of the violence appeared to be “tied up with clan criminality,” including clans with “links to Israel.”

Members of a number of clans in the enclave have clashed with Hamas over the past two years, including the Abu Shabab clan, led by Yasser Abu Shabab, whom Hamas has accused of collaborating with Israel. The Doghmosh clan, one of the biggest and most powerful in Gaza, has also been at odds with Hamas.

Reuters reported that Hamas fighters had clashed with members of Doghmosh on Sunday and Monday, citing security sources. NBC News was not immediately able to verify that reporting.

“There are well-known clans and personalities,” Hanna said. “Anybody at this point who is trying to operate independently outside of Hamas authority in the places where it is present is probably going to have trouble.”

In a statement released on Tuesday following a gathering of Palestinian tribes and clans in the Gaza Strip, some clans warned that protection would be withdrawn from any members “proven to be involved in any violation that threatens our societal security and civil peace.”

They urged groups to “fully adhere to this decision” to keep the peace and to “hand over perpetrators and violators to the competent authorities,” in an apparent reference to Hamas.

“I think it was a stupid strategy for Israel to try to rely on some of these clans,” Ahmed Fouad Alkhatib, head of Realign for Palestine, a project of the Atlantic Council, said. “Hamas made a name for themselves early on by basically breaking a lot of these clans and by having the ability to say we’re bringing law and order.”

The gang violence in Gaza comes as peace efforts have also been complicated by Hamas’ failure to return many of the 28 bodies of hostages killed in captivity.

Hamas said Wednesday that the remaining bodies required “significant efforts and specialized equipment to search for and retrieve.”

Israeli Defense Minister Israel Katz told senior Israel Defense Forces commanders to prepare a military plan to defeat Hamas if the militant group refuses to implement the U.S.-brokered peace plan, according to Katz’s spokesperson.