Can Hamas hold back Islamic State in Gaza?
The Gaza Strip is still reeling from last year's devastating war with Israel, but now there are troubling signs that it faces an internal threat from ultra-conservative militants, some inspired by the Islamic State (IS) group.
In January, protesters carrying the black flags of IS burnt the French Tricolore at a rally against the cartoons of Prophet Muhammad published by satirical magazine Charlie Hebdo.
Gaza's Hamas authorities allowed that to go ahead, wanting to show their own Islamist credentials. But in the last few months, there has been a series of confrontations.
Hamas has taken a tougher stance against IS since it killed about 100 Palestinian in April, beheading two leaders of a Hamas-linked group, in Yarmouk refugee camp in southern Damascus.
At the same time, extremists appear to have been encouraged by IS gains elsewhere in the region.
"We have the Salafist groups here in Gaza pledging their support to Islamic State," says Mukhaimer Abu Saada, politics professor at Gaza's al-Azhar University.
"They very much identify with Islamic State in terms of their ideology and their radical interpretations of Islam and the Koran."
"They are unhappy with Hamas because they believe it has not implemented Islamic law and because Hamas has reached an understanding with Israel, which put an end to the war in the summer of 2014."
'We will never forget'
Hamas blames radical Salafist groups for several small explosions targeting its security forces. Dozens of activists and religious leaders have been arrested and a Salafist mosque destroyed.
Last week, an IS-supporting militant, 27-year-old Younis Hunnar, was killed in a raid by Hamas security forces on his home in Gaza City.
Three rockets have since been fired at Israel and a group calling itself the Omar Brigades said via social media that it was responsible. On Thursday, a fourth rocket was launched but fell short inside Gaza.
While the missiles have not caused injuries, they have drawn Israeli air strikes in response - some targeting Hamas military sites - and endangered a 10-month-long ceasefire between Israel and Hamas.
At the entrance to Mr Hunnar's apartment, bloodstains and bullet holes are still visible. His brother tells me the family no longer want to speak about what happened.
However, on the walls outside, an IS flag has been drawn and there are slogans against Hamas alongside pledges of revenge. Some graffiti reads: "We will never forget your blood while we live."
Salafists appeared in Gaza about a decade ago. They adhere to a strict lifestyle based on that of the earliest followers of Islam.
So far, Hamas, which has its ideological roots in the more moderate Muslim Brotherhood, has been largely able to contain them.
There were tensions in 2009, after a Salafist leader, Abdul Latif Moussa, declared an Islamic emirate in the southern town of Rafah. He was among more than 20 people killed the next day when Hamas forces stormed his mosque and house.
In 2011, after the abduction and murder by Salafists of a pro-Palestinian Italian activist, Vittorio Arrigoni, Hamas also took action to crush the groups.
The number of militant Salafists is estimated to be relatively small - amounting to hundreds or perhaps a few thousand at most.
By contrast, Hamas has some 35,000 security personnel under its military command.
However the latest developments come at a time when the Islamist movement is weaker.
Last year's 50-day conflict killed some 2,200 Palestinians, mainly civilians, according to the UN, and 73 on the Israeli side, mostly soldiers.
Tens of thousands of homes were destroyed and key infrastructure was badly damaged.
There is rising frustration over the failure of Hamas to lift the blockade of Gaza, which Israel and Egypt say they impose for security reasons but which has severely hampered the pace of reconstruction.
Hamas Deputy Foreign Minister Ghazi Hamad insists there is no organisation formally associated with IS in Gaza and that "ignorant people" will be dealt with.
"You'll find some individuals who support their thoughts but I can confirm and assure [you] there is no organisation affiliated to Daesh [Islamic State] or al-Qaeda in Gaza," he says. "We will not allow such radical groups to survive."
"We won't allow anyone to break the ceasefire because it's in the national interests," he adds, in reference to the recent missile fire.
At a security conference in the Israeli city of Herzliya this week, Prime Minister Benjamin Netanyahu said the situation in Gaza "could ignite the region".
He sent a warning to Hamas: "I have a very clear policy - you fire at us, we fire back. Hamas is responsible for non-Hamas rocket fire too."
But some observers see Israel's approach as potentially playing into the Salafists' hands.
"They're trying to challenge Israel and Hamas," Eran Zinger, Israel Radio correspondent, says. "They know that once we see missile attacks coming from Gaza, Israel will have no other choice but to retaliate and this is exactly what they want. They know this will have an effect on Hamas."
For now the Salafists appear to be doing little more than riling and putting pressure on Hamas.
Their fighters are said to lack clear leadership and organisation and have few resources.
However there are fears they could attract disenfranchised militants from inside Hamas's ranks and obtain funds and arms from IS organisations outside, particularly from Egypt's Sinai. That could cause a dangerous escalation.