Israeli riot policemen fire tear gas at Palestinian demonstrators on May 13, 2011 in the East Jerusalem neighbourhood of Issawiya, Israel. Palestinians began marking the “Nakba” or “catastrophe” which befell them following Israel's establishment in 1948. (Photo by Uriel Sinai/Getty Images)

Israeli riot policemen arrest a Palestinian demonstrator during clashes May 13, 2011 in the East Jerusalem neighbourhood of Issawiya, Israel. (Photo by Uriel Sinai/Getty Images)

Palestinian youth throw stones during clashes with Israeli police on May 13, 2011 in the East Jerusalem neighbourhood of Issawiya, Israel. (Photo by Uriel Sinai/Getty Images)

Palestinians pray outside the old city on May 13, 2011 in the East Jerusalem, Israel. (Photo by Uriel Sinai/Getty Images)