European Union officials have launched an investigation after bugging devices were found at offices used by several delegations - including those of France, Germany and the UK.
Extra security measures have been adopted ahead of a meeting of EU leaders in Brussels on Thursday and Friday.
Spanish, Italian and Austrian offices had also been bugged, officials said.
The discovery of the telephone tapping systems was first reported on Wednesday by France's Le Figaro newspaper, which blamed the US.
Officials are reluctant to speculate on who was behind the move. 'I deny that we have identified whoever was responsible, whether it was the Americans, the Russians, the Chinese or whoever. We have launched an investigation, a council official told AFP.
A spokesman for the US mission to the EU declined to comment on the report.
EU investigates mystery buggings
Phone taps found at EU's Brussels HQ [/b]
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