WASHINGTON (AFP) - US President George W Bush has given his national intelligence director greater powers to manage rival US spy agencies as part of an overhaul driven by past intelligence failures, White House documents released Thursday show. The authorities were spelled out in revised executive order 13355, which Bush signed on Wednesday, carrying out reforms enacted four years ago in the wake of intelligence fiascos involving Iraq and the September 11, 2001 attacks. "This is the first significant adjustment in the executive order in several decades," a senior administration official said, speaking on condition of anonymity. Officials said the new order retains bans on assassinations of foreign leaders, limits on human experimentation, and protections of civil rights of US nationals contained in the original order, which was signed in 1981 by then president Ronald Reagan. The most significant changes focus on the role of the director of national intelligence, or DNI, a post created under a 2004 law that took overall responsibility for US intelligence away from the Central Intelligence Agency. The CIA remains in charge of espionage under the revised order, which assigns the agency the role of "functional manager" for human intelligence. The CIA also remains the one agency permitted to conduct covert actions, with the exceptions of the military in time of war or "unless the president determines that another agency is more likely to achieve a particular objective." But the director of national intelligence is responsible for overseeing and advising the president on all ongoing and proposed covert action programs under the revised order. The National Security Council will present proposals for covert action to the president with all dissents, the order said. The DNI is authorised to have access to all information gathered by the 16 intelligence services in the US government, and to decide what agencies can get it, the documents show. That authority is designed to discourage intelligence agencies from refusing to share intelligence that they have collected, a chronic problem. The changes also give the DNI new authorities in the hiring and firing of the heads of intelligence services that fall under the Pentagon and other departments, increasing his influence over the leaders of subordinate agencies. And it authorises the national intelligence director to enter into intelligence and counter-intelligence agreements with foreign governments and international organizations, an area that had been exclusive purview of the CIA. However, the order also says the CIA will "conduct foreign intelligence liaison relationships with intelligence or security services of foreign governments or international organizations." The executive order "clarifies and strengthens the authorities and responsibilities of the Director of National Intelligence," press secretary Dana Perino said in a statement. Earlier speaking outside the White House, President Bush hailed the "durability" of advances in Iraq and announced shorter tours of duty for US soldiers as he hinted more troop reductions could come later this year. He said the US troop surge had helped reduce violence while Iraqi forces built up strength, and pointed to progress in negotiations towards a deal on the continued presence of US troops there. Still, Bush cautioned that the gains could be "reversible," even as Pentagon figures showed that 11 US soldiers were killed in Iraq in July, the fewest to die in a single month since the invasion five years ago. Meanwhile, Iraq's cleric Moqtada Sadr called on the government on Thursday not to sign an accord being negotiated with Washington that will govern the presence of US troops from next year. A US embassy official on Thursday confirmed to AFP that the negotiations were ongoing, describing them as "constructive." In the ongoing violence, three police officers were killed and four others wounded when a suicide bomber tried to ram his car into a police station in the small town of Al-Geyar, about 50km from the violence-ridden northern city of Mosul, police captain Ayhmed al-Jiburi said. Iraqi forces backed by US troops arrested another 14 suspects during a major military sweep aimed at breaking up the Al-Qaeda network in the restive province of Diyala.