Fatah strongman Muhammad Dahlan has branded the ruling Palestinian Hamas movement "murderers and thieves", in a rising war of words between factions.
Muhammad Dahlan claimed Fatah had won back the streets of Gaza
Mr Dahlan, an MP and former security chief and minister, organised Gaza's biggest pro-Fatah rally on Sunday.
Speaking in an Israeli media interview, he said Hamas had lost popular support.
"They have lost the Palestinian street which sees what they have become: A bunch of murderers and thieves who execute... Fatah members," he said.
He added that the show of support on Sunday, attended by thousands of Fatah loyalists, "proved to Hamas that Gaza is not theirs".
Hamas won last year's parliamentary elections for the Palestinian Authority, taking power from Fatah which had dominated Palestinian institutions for decades.
Factional tensions erupted into deadly armed clashes in the Gaza Strip in December, when Palestinian Authority President Mahmoud Abbas, of Fatah, called for early elections.
At least 30 people have died in the fighting over the last month, and more than 100 have been wounded.
After Sunday's rally, Hamas spokesman Fawzi Barhum accused Mr Dahlan of bringing Palestinians to the brink of civil war.
"We remain vigilant in the face of these putschists and their plots," Mr Barhum said at a news conference, quoted by AFP.
Mr Dahlan once enjoyed a high profile career in the Palestinian Authority in both the political and the security sphere.
He is reviled by Hamas and other Islamist groups for a crackdown he instigated against then in the 1990s when the PA was committed to stamping out militant attacks against Israel.
He remains a powerful figure in Fatah, but in the Haaretz interview he denied reports he had been put in charge of Mr Abbas's security forces again.
Instead, he said his task was to build up grassroots support for Fatah in the Gaza Strip, and he claimed the rally in Gaza on Sunday was proof of his success.