BEIJING (AFP) - China's first aircraft carrier embarked on its inaugural sea trial Wednesday, Beijing said. Beijing only recently confirmed it was revamping an old Soviet ship to be its first carrier and has sought to play down the vessel's capability, saying it will mainly be used for training and "research". The voyage comes amid heightened tensions over a number of maritime territorial disputes involving China. The defence ministry said the carrier's first sailing would be brief, and that the ship would afterwards return to the northeastern port of Dalian for more "refit and test work". The United States said Wednesday it would like China to explain why it needs an aircraft carrier amid broader US concerns about Beijing's lack of transparency over its military aims. "We would welcome any kind of explanation that China would like to give for needing this kind of equipment," State Department spokeswoman Victoria Nuland told reporters when asked whether the carrier would raise regional tensions. Andrei Chang, head of the Kanwa Information Centre, which monitors China's military, told AFP it would probably test whether the engines worked, and that on-off sea trials were likely to continue for another year or two. China's People's Liberation Army - the largest armed force in the world - is extremely secretive about its defence programmes. Earlier this year, China announced military spending would rise 12.7 percent to 601.1 billion yuan ($91.7 billion) in 2011. In January it revealed it was developing its first stealth fighter jet, and it is also working on an anti-ballistic missile capable of piercing the defences of even the most sturdy US naval ships. However, Beijing has repeatedly sought to alleviate fears over its pursuit of sophisticated weaponry and the official Xinhua news agency said the new carrier posed no threat to any other country. "Building a strong navy that is commensurate with China's rising status is a necessary step and an inevitable choice for the country to safeguard its increasingly globalised national interests," it said. "Even if China developed an aircraft carrier with full combat capacity in the future, it will not pose any threat to other countries." China only provided the first official acknowledgment of the carrier in June when Chen Bingde, the nation's top military official, gave an interview to a Hong Kong newspaper.