
Rival Palestinian factions Hamas and Fatah resumed their clashes following a weeklong lull in internal violence, with each group kidnapping members of the other.
Security officials say fighting erupted between Hamas and Fatah forces in the Jabaliya refugee camp near Gaza City late Monday.
More than three people were injured in the clashes, officials said.
Reports said Hamas gunmen kidnapped two Fatah members, while Fatah seized 18 Hamas fighters, including seven who were later reported to have been released.
Correspondents in Gaza say Hamas described their initial raid as a routine policing operation carried out by members of the Hamas-controlled interior ministry.
But Fatah claimed that it was a kidnapping operation and seized Hamas members in return.
The recent clashes violate an Egyptian-brokered ceasefire that ended days of internal fighting between Hamas and Fatah on December 17.
Tensions between Hamas and Fatah escalated after Palestinian President Mahmoud Abbas called for early elections last month, a move rejected by Hamas as a "coup."
Meanwhile, a Peruvian photographer working for the Agence France Press news agency was kidnapped Monday by unknown gunmen from downtown Gaza City.
There was no immediate claim of responsibility for the abduction of the photographer, identified by AFP as Jaime Razuri, 50.
Many foreigners have been kidnapped in Gaza over the past two years. Most were released unharmed.
In a separate development, Palestinian fighters fired a mortar shell into Israel early Tuesday, damaging a truck at the Gaza Strip's main cargo crossing.
The truck was transporting building materials to Gaza when it was hit by the mortar at the Karni crossing, the Israeli army said.
There were no casualties reported, and nobody claimed responsibility for the attack.
Karni is the main crossing point for Gaza's imports and exports, and is critical to the Palestinians' fragile economy. Israel often restricts traffic through the vital terminal.
Source: AJP and agencies