Brussels - Belgian police said Thursday they had thwarted a possible terrorist attack by arresting 14 suspect members of al-Qaeda, just hours before European Union heads of state and government were due to meet in Brussels.

The arrests capped a year-long investigation and were the result of 16 early morning raids involving more than 240 counter-terrorism officers in Brussels and Liege.

Police sources said three of the arrested had recently returned from a terrorist training camp in Afghanistan or Pakistan, and that one of them had recently bid his relatives farewell in a video.

Investigators said one of the suspects had just "received the green light to carry out an operation," possibly in Belgium or elsewhere in Europe, the on-line edition of Le Soir newspaper reported.

But prosecutors said they could not exclude the possibility that the alleged terrorists had been planning to target the EU summit.

"Given the fact that the EU summit is taking place at this time in Brussels, obviously we had no choice but to act today," Belgian federal prosecutor Johan Delmulle was quoted as saying.

Belgian Prime Minister Yves Leterme praised the operation, saying the police had taken the threat "seriously."