BRUSSELS- NATO's secretary-general said on Monday he had seen evidence convincing him Syrian authorities were behind a deadly chemical weapons attack and said it would send a "dangerous signal to dictators" if the world did not respond firmly.However, Anders Fogh Rasmussen said it was up to individual NATO countries to decide how they would respond to the attack and he did not envisage any NATO role beyond existing plans to defend NATO member Turkey, which borders Syria."I have been presented with concrete information and, without going into details, I can tell you that personally I am convinced, not only that a chemical attack has taken place ... but I am also convinced that the Syrian regime is responsible," Rasmussen told a news conference.US President Barack Obama has said he will seek congressional authorization for punitive action against Syrian President Bashar Assad after what Washington said was a sarin gas attack on Aug. 21 that killed more than 1,400 people.Rasmussen said there was "agreement that we need a firm international response in order to avoid that chemical attacks take place in the future. It would send, I would say, a dangerous signal to dictators all over the world if we stand idly by and don't react."But Rasmussen said he saw no further role for NATO in the Syria crisis, beyond defending Turkey.Crisis in Syria - full JPost.com coverage"If a response to what has happened in Syria were to be a military operation, I'd envisage a very short, measured, targeted operation, and you don't need the NATO command and control system to conduct such a short, measured, tailored, military operation," he said. Meanwhile, the USS Nimitz aircraft carrier and four other ships in its strike group moved into the Red Sea early on Monday, US defense officials said, describing the move as "prudent planning" in case the ships are needed for military action against Syria.The officials said the Nimitz entered the Red Sea around 6 a.m. EDT (1000 GMT), but the strike group had not received any orders to move into the Mediterranean, where five US destroyers and an amphibious ship remain poised for possible cruise missile strikes against Syria.Moving the Nimitz into the Red Sea was aimed at putting more US assets in place if they are needed to support what US officials still describe as a limited attack against Syria after it used chemical weapons against civilians."It does place that strike group in a position to respond to a variety of contingencies," said one official, who was not authorized to speak publicly.The nuclear-powered Nimitz is accompanied by the Princeton, a cruiser, and three destroyers - the William P. Lawrence, Stockdale and Shoup, according to the officials.They said there had been no change regarding six US Navy ships now in the eastern Mediterranean, but military planners were reassessing the situation given a delay in the cruise missile strikes that had been expected this past weekend.President Barack Obama on Saturday backed off imminent strikes by five destroyers off the coast of Syria until Congress had time to vote its approval. Defense officials said the delay gave them more time to reassess which ships and other weapons will be kept in the region - and whether some may be allowed to leave. Congress returns to Washington Sept. 9. The US Navy doubled its presence in the eastern Mediterranean in the past week, effectively adding two destroyers to the three that generally patrol the region.The destroyers are carrying a combined load of about 200 Tomahawk missiles, but officials say a limited strike on Syria could be accomplished with half that number.