BEIJING: US President Donald Trump approved a plan giving the country's navy greater freedom in operating in the South China Sea and put pressure on China's efforts to enlarge its military presence by artificially building reefs and atolls in the area.The move is seen as a challenge to Beijing's maritime claims over most of the South China Sea and its attempts to overrule overlapping claims by five other countries, Vietnam, Malaysia, Indonesia, Brunei and the Philippines.The US move will keep China's expanding navy busy in the South China Sea and make it difficult for Beijing to deal with its territorial disputes with other countries such as India and Japan at a time when the Communist Party is preparing for a conclave which will see major political changes.The new plan, which was submitted by US defence secretary Jim Mattis, involves a full-year schedule of when US navy ships will sail through contested waters. The US navy will now enjoy a lot more freedom than it did during the Obama administration, which insisted on the National Security Council approving major operational decisions.The decision came soon after Chinese warships began moving towards the Baltic Sea for a joint naval exercise with Russian navy on Friday. This is seen as an attempt to reassure Moscow that China would stand by it in the case of threats from western powers, analysts said."By sending its most advanced guided-missile destroyers, China is expressing its sincerity to Russia and also sends a strong signal to other countries who plan to provoke us," Li Jie, a Beijing-based navy expert told the state-run Global Times.China lost its case over the South China Sea at the International Court at The Hague, which deemed Beijing's claims as unlawful and excessive. But China has rejected the validity of the verdict. Analysts said China plans to expand its air defense and identification zone into the western Pacific and build a blue water navy to rival that of the US.