HONG KONG (AFP) - Hong Kong police said Monday they have stepped up security over the visit of the US aircraft carrier from which Osama bin Laden was buried at sea, as the crew remained tightlipped about the incident. The nuclear-powered USS Carl Vinson and its support ships arrived in the southern Chinese city on Sunday for a port call, after local media highlighted security concerns and fears of a militant attack following the Al-Qaeda leader's death earlier this month. Police said they had stepped up patrols in key neighbourhoods such as the rowdy Wan Chai entertainment district, which many of the 7,000 sailors are expected to visit during their four-day shore-leave. The ship is scheduled to leave on Wednesday. "We will take action if there is any suspicious person or objects. We will take extra care to avoid any risk of a terror attack," a police spokesman told AFP, adding that the threat of a terrorist attack remained at "moderate" level. Sailors approached in several districts of the city declined comment, saying they had been ordered not to speak about bin Laden's burial. One sailor told The Standard newspaper he only found out from news reports: "My jaw dropped. It was a great shock." On Sunday, Rear Admiral Samuel Perez also declined to answer questions concerning bin Laden's burial, but said he was not worried about the safety of US military personnel in the city. "The port protection measures we take here in Hong Kong are the normal ones we take for all of our liberty ports," he told reporters, describing the stopover as a "normal port visit." "The Hong Kong police and the entire city of Hong Kong has been very welcoming to us and have provided us very strong assurances that they will keep our sailors and our ships safe ... we feel very safe here in Hong Kong". When asked if the ship conducts frequent sea burials, Perez said: "Yes, as a matter of fact, we do. Sailors who request to be buried at sea, we do take them out (to be buried)."