By Martin Patience
BBC News, Jerusalem
The violence during a rally to mark the third anniversary of Palestinian leader Yasser Arafat's death illustrates the deadly tensions between the two main Palestinian political factions.
Fatah supporters reportedly began taunting the Hamas forces
Six Palestinians were killed and dozens other injured as clashes broke out between Hamas and Fatah supporters at the Gaza memorial. Both sides laid the blame for the violence at each other's door.
Ever since the bloody Hamas takeover in June, the Islamic movement has pursued an aggressive law-and-order agenda, barring demonstrations, and sometimes brutally cracking down on its rival, Fatah.
But Hamas permitted Monday's commemoration of Yasser Arafat - also the former Fatah leader - hailing him as a national figure.
Hundreds of thousands of Palestinians, waving yellow Fatah flags and carrying portraits of the late leader, marched into Gaza City, says the BBC's Gaza producer Hamada Abu Qammar.
But for Fatah leaders, and many of those in attendance, this was an excellent opportunity to protest against Hamas rule in Gaza. Last year's anniversary was a smaller affair.
At speeches given during the rally, Zakaria al-Agha, the Fatah chief in Gaza, directly challenged the Islamist movement.
"We say to Hamas and these armed militias, stop your crimes," he said, reading a statement by Palestinian President Mahmoud Abbas.
"These crimes will not shake our determination."
Parts of the crowd chanted at Hamas security members "Shia, Shia" - seen as an insult and accusing them of being a proxy for Shia Iran and its ally Syria.
The rally was a chance for people to vent their anger at Hamas
Many observers see the Gaza Strip as caught in the middle of a wider power struggle between the West and Iran for greater control in the Middle East.
Israel, the US, and Europe have embraced Mr Abbas and his Fatah party, which predominates in the West Bank.
Mr Abbas, along with Israeli Prime Minister Ehud Olmert, is due in Annapolis later this month for a Middle East conference.
In contrast Hamas, which won the parliamentary elections in 2006, has been internationally ostracised for its refusal to recognise Israel and renounce violence.
The Jewish state declared Gaza a "hostile entity" in September, in what Israeli officials said was a response to the almost daily rocket fire from the territory.
The sanctions that were lifted in the West Bank in June, when Mr Abbas formed an emergency government that excluded Hamas, have been tightened in Gaza.
Gaza's economy has largely collapsed, access to and from the territory is tightly controlled, and the majority of the population live below the poverty line, according to the UN.
Some political analysts say that the dire situation in Gaza is weakening support for Hamas.
"People were showing their anger against Hamas at this rally," says Bassam Nasser, director of the Palestinian Centre for Democracy and Conflict Resolution.
"They were also saying to the West that Gaza isn't just Hamas and the closures must be lifted."
But for now, that appeal seems to be falling on deaf ears.
Hamas has repeatedly called for reconciliation talks with Fatah. But Mr Abbas says that Hamas' takeover in Gaza must be reversed before that can happen.
Neither side is backing down and nor does there appear to be a leader capable of unifying the two factions.