Spanish police arrested Tuesday four men over their alleged links to suspects held in Belgium over their alleged involvement in the Brussels airport and metro attacks last year, officials said.
The four were among eight people arrested in a vast operation targeting suspected Islamic extremists carried out in conjunction with Belgian police in the northeastern region of Catalonia, Catalan police said.
"Four of those who were detained have links with people arrested for the attacks carried out at Brussels airport and metro," a spokesman for Catalonia's regional police force told AFP.
It is not clear if the four were directly involved in carrying out the Brussels attacks, the spokesman added.
Belgium has been on high alert since March 22 last year when suicide bombers attacked Zaventem airport and Maalbeek metro station, killing 32 people and leaving more than 320 wounded.
The attacks were led by an Islamic State cell that was also responsible for the carnage in Paris in November 2015.
The men arrested in Catalonia "may have participated or cooperated in past actions" and may have travelled to Belgium, Catalonia's regional interior minister Jordi Jane told radio Rac1.
The eight suspects arrested on Tuesday lived in Catalonia and are aged between 31 and 39, the head of Catalan police, Josep Lluis Trapero, told TV3.
Some of the suspects are linked to organised crime groups and drug trafficking, he added.
Police raided 12 properties in five Catalan cities, including the regional capital Barcelona, as part of the operation.