Spain recently expelled two American spies who infiltrated the Spanish intelligence services by recruiting two agents from the National Intelligence Center (CNI), reports El Pais daily.

Spanish agents recruited by Washington are accused of passing classified information to the United States and have been arrested, the news site El Confidencial reported on Monday. The left-wing Spanish government simply confirmed the existence of the case without giving details.

Speaking informally to a group of foreign journalists on Tuesday, Spain’s Socialist Prime Minister Pedro Sanchez acknowledged the incident had caused tensions between Madrid and Washington, but assured them they were gone, again giving no details, AFP reported.

According to the daily newspaper El País, “At least two American agents assigned to the US Embassy in Madrid, who were directly involved in the recruitment of CNI spies, have been secretly expelled from Spain.”

Asked by AFP, Spain’s Foreign Ministry said it had “no comment” on the matter and neither confirmed nor denied the newspaper’s report.

The Ministry of Defense, on which the CNI depends, did not respond to AFP by midday.

The extreme discretion of the authorities that is common in espionage cases was heightened by the new and delicate nature of the business, given that the United States was a close ally of Spain.

According to El País, citing government sources, Spanish Defense Minister Margarita Robles summoned the American ambassador, Julissa Reynoso, to demand an explanation, while her counterpart in foreign affairs, José Manuel Albarez, called the diplomat to express his concerns about the Spanish government.

The two Spanish agents were allegedly arrested in September after the CNI found they had access to classified documents for which they did not have the necessary authorization.

It is not known what information was given to American intelligence.

The US government also declined to comment.