Portuguese police have seized half a tonne of explosives and primed bomb devices in a cache, which Spanish authorities suspect belonged to the armed Basque separatist group Eta.
"Around half a tonne of explosives and bomb-making equipment" were found in the garage of a house in Casal da Averela, near the central Portuguese town of Obidos, Helder Barros, a local police chief, told reporters on Friday.
"The material was stored in secure conditions which indicates the work of professionals," he said, adding that "several of the explosives were ready to be used."
Portuguese police also found "some maps of Spain" and a small van containing construction material, fake license plates and two detonators, Jose Almeida Rodrigues, head of Portugal's judicial police, told a news conference at the anti-terrorism centre in Lisbon.
Rodrigues did not name any particular group, but a Spanish anti-terror source said earlier that the explosives found over the border in Portugal "may have been used by Eta."
On Thursday, neighbours alerted the police after noticing that the house, recently rented by two men speaking Spanish, seemed to have been abandoned in a hurry, Nelson dos Santos, the local Portuguese police chief, said.
Police were looking for the two men.
The discovery of the explosives came less than a month after Portuguese police arrested two suspected members of Eta who had fled Spanish authorities in the north of Portugal.
Alfredo Perez Rubalcaba, the Spanish interior minister, recently indicated that Eta could be looking to set up a rear base in Portugal to launch attacks in Spain.
Eta is blamed for 828 deaths in a 41-year campaign for independence in the Basque region of northern Spain and southwestern France.
It appears on several terrorism blacklists, including those of the European Union and the United States.