(Adds Hamas arrest of Fatah suspects, paragraph 8)

By Mohammed Salem

GAZA, July 25 (Reuters) - A bomb exploded next to a car used by the armed wing of Hamas in the Gaza Strip on Friday, killing three gunmen and a girl, the ruling Palestinian Islamist group and medical officials said.

The attack was the third of its kind in a day, making for one of the biggest flare-ups in internal violence since Hamas routed the forces of Palestinian President Mahmoud Abbas's secular Fatah faction to seize control of Gaza a year ago.

Abbas, finding his authority limited to the occupied West Bank, split with Hamas and revived peace efforts with Israel. He recently sought reconciliation with his Islamist rivals but they have balked at his precondition that they give up Gaza.

The Hamas armed wing issued a statement blaming "members of the fugitive party" -- a derogatory term for Fatah -- for Friday night's blast at a major junction outside Gaza City.

"We have information that some elements are planning to carry out bombings against the interests and leaders of Hamas in order to sow anarchy," said senior Hamas leader Khalil al-Hayya, whose son, himself a gunman, was wounded in the explosion.

Nineteen other Palestinians were hurt, medical officials said, many of them passers-by on their way to the beach.

Fatah officials in the West Bank could not immediately be reached for comment on the Hamas accusations.

Hours later, Hamas said a car belonging to one of its members was torched in the southern Gaza town of Rafah. There were no casualties. Hamas police then stormed a local home and arrested two brothers, both Fatah members, Hamas said.

The factional violence has eclipsed Israeli-Palestinian fighting in Gaza, where an Egyptian-brokered truce has largely held since last month despite some violations on both sides.

The ceasefire stoked occasional intra-Palestinian tensions as Hamas has sought to prevent other groups from firing rockets across the border into Israel.

Before dawn on Friday, bomb blasts rocked a cafe and the home of Hamas politician Marwan Abu Rass in Gaza City. A passer-by was killed outside the cafe.

Hamas Interior Ministry spokesman Ehab al-Ghsain accused Fatah of being behind the attack on Abu Rass's home, which caused no casualties. Fatah denied involvement. (Reporting by Nidal al-Mughrabi; Writing by Dan Williams; Editing by Richard Williams)

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