RAMALLAH (AFP) - Palestinians protested across the occupied territories on Thursday on the 60th anniversary of the "catastrophe" of the birth of Israel in 1948 and the exodus of hundreds of thousands of refugees. Israeli troops fired into the air to break up a rally at the border between Gaza and Israel while sirens sounded across Ramallah as thousands joined a protest demanding the "right of return" for some 4.5 million UN registered refugees in camps across the Middle East. Demonstrators waved Palestinian flags and released 21,915 black balloons - one for each day since Israel's creation - to darken the skies over Jerusalem ahead of Bush's speech. Palestinian President Mahmoud Abbas said he is determined to end Israel's occupation of Palestinian land, labelling it "mankind's shame". He also said his hands were extended in peace, as Palestinians mark the "catastrophe" of Israel's creation. Israel's security depends on the creation of a Palestinian state, he stated. "On this good and beloved land live two peoples. One celebrates its independence and the other grieves in the commemoration of its Naqba," Palestinian President Mahmud Abbas said in a televised speech."Israel's security is linked to our independence and our security, and the continuation of the occupation and the persistence of the Naqba will not bring security to anyone." "We renew our commitment to our principles of peace, the peace that will lead to an end to the occupation over all Palestinian lands occupied in 1967, and at their heart holy Jerusalem," Abbas said."The settlements and their continuation is destroying the opportunity for peace," he said, adding that all settlement projects including those in annexed east Jerusalem must be halted. About 3,000 people gathered in the heart of the northern West Bank city of Nablus holding keys - real and symbolic - to abandoned houses in what is now Israel and burning a US flag to protest Bush's visit.In the besieged Gaza Strip, where Hamas seized power nearly a year ago, supporters of the Islamist movement marched to the Erez crossing with Israel to protest what they derided as the "new Naqba" - a crippling months-old blockade of the territory. Hundreds of demonstrators marched to a gathering point a few kilometres from the crossing, waving Palestinian flags and green Hamas banners and demanding that Israel lift the blockade. Dozens of members of the Hamas-run police force in Gaza sealed the main road to the crossing, but later in the afternoon dozens of women and children walked towards the border, with some of the children throwing rocks. Israeli troops fired in the air and launched tear-gas bombs to disperse the group before it reached the crossing, according to witnesses. The anniversary is a bitter occasion for Palestinians, particularly the 4.5 million refugees from 1948 and their descendents, still living in camps in Jordan, Syria, Lebanon, the West Bank and the besieged Gaza Strip. "Sixty years have passed since the Naqba of our people and the uprooting of hundreds of thousands of our sons from their homeland, their houses, and their lands," said Abbas, himself a refugee from the Israeli town of Safed. "Our people still bear the smouldering embers of our dreams, which resemble the dreams of all people, to return to their homes and establish an independent state," he said. "The Palestinian people will enjoy liberation and peace." An Israeli air strike on the Gaza Strip killed two Hamas members and wounded four late on Wednesday, Palestinian medical sources said.