Undercover Israeli policemen together with policemen detain a Palestinian during clashes in the East Jerusalem neighbourhood of Issawiya May 13, 2011. The police are on high alert ahead of "Nakba Day" (Catastrophe), marked on May 15 to commemorate the expulsion or fleeing of hundreds of thousands of Palestinians from their homes in the war that led to the founding of Israel in 1948. REUTERS/Ammar Awad (JERUSALEM - Tags: POLITICS CIVIL UNREST)