BILBAO, Spain — Spanish police on Tuesday discovered nearly one ton of explosives in an arms cache of the armed Basque separatist group ETA, police said.

The explosives were found in a country house in the Basque locality of Legorreta, where two suspected ETA members were detained earlier Tuesday.

The arms cache was one of the biggest ever attributed to ETA in Spain. It was discovered only three months after ETA announced a “”permanent”” cease-fire in January.

The two detainees, who are brothers, were suspected of supplying ETA with weapons and explosives.

The arrests followed those of two other ETA suspects in central France on Sunday. The two had fled following an exchange of gunfire in which a police officer was wounded on Saturday.

The shootout was criticized by Bildu, a radical Basque separatist alliance that wants to participate in the May 22 local elections.

Bildu said the “”incident”” went against the cease-fire declared by ETA. Prime Minister Jose Luis Rodriguez Zapatero’s government, however, did not find the criticism sufficient to guarantee Bildu the right to contest the elections.

The government says Spain will only authorize radical separatist parties that clearly condemn ETA violence.

The government intends to investigate whether Bildu candidates include people linked to Batasuna, ETA’s illegal political wing.

Batasuna and its entourage recently launched a new radical separatist party, Sortu, which was then barred by the Supreme Court from contesting the elections.

The government now suspects that Bildu, the core of which is made up of two legal separatist parties, could act as a new cover for Batasuna, which was banned in 2003.

ETA declared a cease-fire in September and reinforced it in January. The government has nevertheless maintained a hard line against the group, 35 of whose suspected members have been detained this year.

ETA, which has killed about 850 people since 1968, is listed as a terrorist organization by the European Union and the United States.