The suspects were using a jihadist website to plan an attack on an unspecified target, police said.

"Long months of undercover investigation" led to the arrests, the authorities said. It was "clear to us that the target was Belgian soil, just not clear enough to say where and when," Belgian public prosecutor Lieve Pellens told CNN.

Seven of the arrests were in Antwerp, Belgium, she said. One was in Aachen, Germany, and the other three were in the Netherlands. Those arrested are Belgian, Dutch, Moroccan and Chechen, authorities said.

A senior European counter-terrorism official told CNN that members of the group arrested in Antwerp, and their associates in Germany and the Netherlands, had discussed targeting Jews in Belgium as well as NATO vehicles in the country. However, officials say no specific targets appear to have been identified.

CNN