(Adds quotes, details) WASHINGTON, Feb 2 (Reuters) - The quartet of Middle East peace mediators on Friday voiced its "deep concern" about violence between rival Palestinian factions that has killed at least 21 Palestinians in the last 24 hours. The group, which includes the European Union, the United Nations, the United States and Russia, also appeared to reaffirm an international aid embargo against the Hamas-led Palestinian government unless it renounces violence, recognizes Israel and respects past peace deals. "The quartet expressed its deep concern at the violence among Palestinians and called for respect for law and order," U.N. Secretary-General Ban Ki-moon said, reading a statement on behalf of the group, which met for about two hours. Fighting between Palestinian factions escalated across Gaza on Friday, killing at least 15 people as Hamas overran compounds used by Palestinian President Mahmoud Abbas's forces and two major universities were set ablaze. At least 21 Palestinians have been killed and more than 200 wounded in the last 24 hours of internal fighting. "The quartet called for Palestinian unity in support of a government committed to nonviolence, recognition of Israel and acceptance of previous agreements," Ban added. "The quartet reaffirmed that these principles endure." On Jan. 30, 2006 the quartet made international aid to the Hamas-led government contingent on its accepting the three principles.
