EU leaders warn U.S. spying scandal may hamper fight against terror

European leaders warned Friday that reports of widespread spying on world leaders by the U.S. National Security Agency have raised "deep concerns" among Europeans and could affect the cooperation needed for effective intelligence gathering.

"A lack of trust could prejudice the necessary cooperation in the field," the leaders said in a joint statement issued at the conclusion of a two-day European Union summit in Brussels, Belgium.

Spanish Prime Minister Mariano Rajoy announced that Madrid has summoned U.S. Ambassador James Costos over the matter. The U.S. Embassy in Madrid declined to comment, saying that Rajoy's statement stands for itself.

German Chancellor Angela Merkel said the assertions that the U.S. National Security Agency spied on her and other world leaders had "severely shaken" relationships between Europe and the United States, and trust will have to be rebuilt.

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"Obviously, words will not be sufficient," Merkel told reporters Thursday in Brussels. "True change is necessary."

Germany and France intend to seek talks with the United States "with the aim of finding before the end of the year an understanding on mutual relations in that field," the EU leaders' statement said. Other nations are welcome to join these talks, it noted.

French President Francois Hollande, speaking in Brussels, said the aim of the talks would be to establish a joint cooperation framework with the United States "so we put an end to these practices and ... these monitoring schemes."

Hollande said there is an "ongoing dialog" with the United States over its past actions, but the priority is establishing a "code of conduct" for the present and future.

This is essential because France and its European allies "cannot accept" the kind of monitoring which has gone on, whose purpose "is not just political -- it is mainly an economic issue," Hollande said.

"It is relevant to the markets, to the prices, to the mergers and acquisitions. This is where the monitoring may have the highest impact -- on jobs in particular," he said.

The main purpose of intelligence efforts is tackling terrorism and ensuring security, he said, but no one should have to fear their personal data being used.

Meanwhile, Merkel is under pressure to take a strong stance back home, where her conservative party is in negotiations with the Social Democratic Party, known as the SPD, to form a grand coalition government.