Spanish police detained a man and seized more explosives yesterday as part of an operation against the Basque separatist group ETA, an anti-terrorism source said.

The arrest is connected to Tuesday’s detention of two brothers suspected of belonging to an ETA commando unit called Erreka and the seizure of hundreds of kilograms of explosives in the northern town of Legorreta.

The man was detained in the Basque city of San Sebastian, the source said, without specifying if he was suspected of belonging to ETA.

A still undetermined amount of explosives was found in the region as part of the police investigation, the source added.

Police on Tuesday found 850 kilograms of ammonium nitrate fertiliser, 13.5 kilograms of the explosive pentrite and detonators in their pre-dawn raid at Legorreta.

It was the biggest explosives cache to be confiscated by police in Spain since 1999.

That same day, police detained José Aitor Esnaola, 40, and Igor Esnaola, 36, on suspicion they belonged to ETA.

Their arrest came three days after a French policeman was wounded in an armed exchange in the Creuse region of southwestern France. A couple was later detained on suspicion of belonging to ETA.

ETA is blamed for the deaths of 829 people in its four-decade campaign of bombings and shootings to force the creation of an independent Basque homeland in northern Spain and southwestern France.