Belgian authorities have lowered their terror threat alert to the second-highest level in the capital Brussels, calling a threat "possible and likely".

Peter Mertens of the Belgian crisis centre said that the threat assessment now stood at the same level throughout the country.

Since Saturday morning, Brussels - home to the European Union and Nato headquarters - had been wary of a threat that was considered "serious and imminent".

The lowering of the threat level came as a surprise, since the government had said that it would likely keep the highest threat level in the capital through the weekend.

On Sunday night, Belgian police carried out a series of raids that the government said were linked to a possible imminent attack like those in Paris on November 13, which killed 130 people.

No firearms or explosives were found and 15 of the 16 detainees had to be released the following day.

Belgian authorities raided three more places outside of Brussels on Thursday which they said are linked to the Paris attacks, but made no arrests.

After raiding a house near southern Sambreville, 80 kilometres (50 miles) south of the capital, they launched two more raids in Verviers, 125 kilometres (80 miles) east of the capital.

Verviers was already the scene of a bloody stand-off in January when two suspects were killed by security forces in a shoot-out. The government said at the time it had averted an imminent attack.

Belgian authorities already have five suspects in prison facing terrorism charges related to the Paris attacks.

At least one Belgian fugitive, Salah Abdeslam, is on the run while another Belgian man, Abdelhamid Abaaoud, who was suspected of orchestrating the attacks, was killed in a police raid north of Paris.