Qaeda Friday confirmed the killing of Osama Bin Laden and vowed revenge, saying that Americans' “happiness will turn to sadness.” The statement was the first by the network since its leader was slain in a US commando raid against his Pakistani hideout. The statement, written in typical Al-Qaeda style and in the name of the organization's General Command, seemed mostly intended to reassure followers that the group remains vigorous and intact. The statement was dated Tuesday, the day after Bin Laden's death. Its authenticity could not be independently confirmed, but it was posted on militant websites Friday by the Al-Fajr Center, Al-Qaeda's online media distribution network. “The blood of Sheikh Osama Bin Laden, God bless him, is too precious to us and to all Muslims to go in vain,” the statement said. “We will remain, God willing, a curse chasing the Americans and their agents, following them outside and inside their countries.” The confirmation by Al-Qaeda should remove doubt among all but the most die-hard conspiracy theorists that Bin Laden is in fact dead. Earlier in the day, hundreds of members of Islamic parties protested in several Pakistan cities against the US raid. Many chanted “Osama is alive” and blasted the US for violating the country's sovereignty. Security officials in Europe say there is no specific plot to justify raising the threat level there. But one of their biggest fears is the possibility of a Mumbai-style attack like the 2008 shooting spree that killed 166 people and paralyzed India's business capital for days. More than 100 protesters gathered Friday outside the US Embassy in London shouting, “USA, you will pay!” and warning of revenge attacks. Interpol has asked law enforcement agencies in some 188 countries to be on alert for retaliatory attacks. UN rights experts press US over killing Meanwhile, UN human rights experts on Friday pressed the United States for full disclosure of the facts surrounding the killing of Bin Laden because of the example such action could set. “Actions taken by States in combating terrorism, especially in high profile cases, set precedents for the way in which the right to life will be treated in future instances,” said the UN special rapporteur on counter terrorism measures, Martin Scheinin, and the rapporteur on extrajudicial and summary executions, Christof Heyns. “In respect of the recent use of deadly force against Osama Bin Laden, the United States of America should disclose the supporting facts to allow an assessment in terms of international human rights law standards.” “For instance it will be particularly important to know if the planning of the mission allowed an effort to capture Bin Laden,” they added in a statement.