BRUSSELS (Reuters) - Countries must be free to pass through the South China Sea, the European Commission said on Wednesday, in its first diplomatic admonishment of Beijing after Chinese jets intercepted a U.S. military plane over the contested waters last month.

Chinese dredging vessels are purportedly seen in the waters around Mischief Reef in the disputed Spratly Islands in this still image from video taken by a P-8A Poseidon surveillance aircraft provided by the United States Navy May 21, 2015. REUTERS/U.S. Navy/Handout via Reuters

The Commission avoided directly criticizing Beijing, a major trade partner, but warned in a new policy document that it opposed “unilateral actions that could alter the status quo and increase tension”, in a sign of concern at China’s construction and militarization of islands in the South China Sea.

“The EU wants to see freedom of navigation and over flight upheld in the East and South China Seas,” the EU executive said in its document, which is aimed at framing the bloc’s China policy over the next five years.

EU governments must still approve the document.

While the European Union says it is neutral in the South China Sea dispute between China and other Asian nations, Washington has been urging Brussels to speak out against Beijing’s claim to almost all the South China Sea.

The United States says Beijing is taking a predatory approach to a vital trade waterway where Vietnam, Malaysia, Brunei, Taiwan and the Philippines have rival claims.

An international court in The Hague is expected to rule soon on China’s claims in a case brought by the Philippines, although Beijing says it does not respect the court’s jurisdiction and the United Nations body does not have powers of enforcement.

In a further sign of tensions, a senior Indonesian official said his country’s president would travel to the Natuna Islands for the first time on Thursday to assert Jakarta’s sovereignty after Beijing said it had an “overlapping claim” over nearby waters.

In one of a series of recent encounters, two Chinese fighter jets intercepted a U.S. military reconnaissance aircraft over the South China Sea in May, demanding that Washington end surveillance near China.

The interception came a week after China scrambled fighter jets as a U.S. Navy ship sailed close to a disputed reef in the South China Sea, through which more than $5 trillion in global trade passes every year.

“The large volume of international maritime trade passing through that area means that freedom of navigation and over flight are of prime importance to the EU,” the Commission said.

“The EU should encourage China to contribute constructively to regional stability ... and support for the rules-based international order,” it said.

Despite the Commission’s careful language, the EU is increasingly concerned by the tensions and French Defense Minister Jean-Yves Le Drian called this month for “regular and visible” European patrols in the South China Sea.