Prosecutors decided Tuesday to begin gathering evidence about the alleged massive spying operations conducted by U.S. intelligence agencies in Spain, officials told Efe.

The goal of the probe is to determine whether criminal acts were committed in light of what is known so far about the spying, an investigation should be opened into the matter and Spain has jurisdiction to prosecute.

Spanish Foreign Minister Jose Manuel Garcia-Margallo warned the United States on Monday that confirmation of the reports of massive spying could lead to "the rupture of the climate of trust" between Madrid and Washington.

Garcia-Margallo's warning to Washington came on the same day that U.S. Ambassador to Spain James Costos was summoned to the Foreign Ministry to discuss the spying allegations with Spanish Secretary of State for the European Union Iñigo Mendez de Vigo.

Mendez de Vigo met with the U.S. ambassador because Garcia-Margallo was on an official visit to Poland.

Costos made a commitment to clear up any "doubts" Madrid might have about the alleged spying by the United States in Spain and vowed to keep the "communications open" with Spanish officials.

Garcia-Margallo said Tuesday he was convinced that the United States would "provide the necessary and pertinent explanations" about the alleged spying, "as befits a relationship between allies."

Reports over the past few days in the Spanish press said the U.S. National Security Agency, or NSA, monitored millions of telephone calls in Spain.

The NSA intercepted more than 60 million telephone calls in Spain between December 2012 and January 2013, the El Mundo newspaper reported on Monday, citing some of the documents leaked by former U.S. intelligence operative Edward Snowden.

The NSA also monitored people's activities on the Internet, e-mails and social-networking sites, such as Facebook and Twitter. EFE