BRUSSELS (Reuters) - The European Union sided with Washington on Friday over a U.S.-Chinese patrolling incident in the South China Sea, in a move that may affect Brussels' discussions with Beijing at next week's Asia-Europe Meeting (ASEM) of foreign affairs ministers.

On Tuesday, a U.S. warship sailed within 12 nautical miles of one of Beijing's man-made islands in the contested Spratly archipelago, triggering a sharp reaction from China.

"The U.S. are exercising their freedom of navigation," a senior EU official said at a briefing, chiming with the U.S. line.

A U.S. Navy spokesman had said that the patrol was part of the U.S. freedom of navigation operations meant to "protect the rights, freedoms, and lawful uses of the sea and airspace guaranteed to all nations under international law".

The EU is concerned about Beijing's plans to build new islands in contested waters, the EU official said, a statement that may be welcomed by other Asian nations opposing China's claims to almost the entire South China Sea.

Vietnam, the Philippines, Taiwan, Malaysia and Brunei contest China's sovereignty over parts of one of the world's busiest sea lanes.

"Whilst not taking a position on claims, the EU is committed to a maritime order based upon the principles of international law, in particular as reflected in the United Nations Convention on the law of the Sea (UNCLOS)," an EU foreign affairs spokesman said in a statement.

The EU has been nursing relations with Beijing, hoping to attract Chinese funds to relaunch the bloc's sluggish economy and has been negotiating a bilateral investment and trade deal.

In defiance of Washington, EU governments have also decided to join the Chinese-led Asian Infrastructure Investment Bank (AIIB).

European and Asian foreign affairs ministers gather in Luxembourg next week for ASEM, a regular event that brings together all 28 EU countries and 21 Asian nations, including China, Vietnam and the Philippines.

(Reporting by Francesco Guarascio; Editing by Louise Ireland)