Palestinian forces have arrested two fighters over rocket attacks on Jewish settlements in the Gaza Strip. The arrests come after President Mahmud Abbas made a pledge to use an "iron fist" to enforce a truce, security sources said on Friday. They were the first arrests by the Palestinian authorities over ceasefire violations since Abbas won agreement from armed groups to respect the truce at a meeting in March. A Palestinian security source said two members of the al-Aqsa Martyrs Brigades, part of Abbas' ruling Fatah movement, were arrested by the Preventive Security Force on Thursday. They were being questioned about rockets fired at Gaza settlements that Israel plans to evacuate in coming months. A spokesman for the brigades said: "We urge the Palestinian Authority and Abbas to release our two fighters." Abbas, in his toughest pledge yet to enforce the ceasefire, told police two days ago that they should use force to prevent fighters from flouting the truce, which has raised hopes for peacemaking after four and a half years of a Palestinian uprising.