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“This is not a situation in which we are rifling through the ordinary emails of German citizens, or American citizens, or French citizens or anybody else,” Mr. Obama said. “This is not a situation where we simply go into the Internet and start searching any way that we want.”

Mr. Obama said the information retrieved by the NSA “applies very narrowly,” with secret court supervision, to leads gathered from other intelligence sources. He also defended the programs as necessary to thwarting terrorist plots.

“As a consequence, we’ve saved lives,” Mr. Obama said. “We know of at least 50 threats that have been averted because of this information, not just in the United States, but in some cases threats here in Germany. So lives have been saved, and the encroachment on privacy has been strictly limited by a court-approved process.”

Mrs. Merkel agreed, saying that “there were quite a lot of instances where we were getting very important information from the United States.” But she added, “There needs to be a balance; there needs to be a proportionality between upholding security and safety of our people and our country.”

The president also addressed Afghan President Hamid Karzai’s announcement Wednesday that he is suspending talks with the U.S. on a proposed security deal as a protest of being left out of negotiations between the Obama administration and the Taliban forces fighting the Kabul government.

“We had anticipated at the outset there were going to be some areas of friction, to put it mildly,” Mr. Obama said. “There’s enormous mistrust. We’re in the middle of a war, and Afghans are still being killed.”

But he said the U.S. still believes there must be “a parallel track” to look at the prospects of political reconciliation in Afghanistan.

“President Karzai himself recognizes the need for political reconciliation,” Mr. Obama said, adding that he hopes “the process will proceed.”

In a terse statement from his office, Mr. Karzai said negotiations with the U.S. on what American and coalition security forces will remain in the country after 2014 have been put on hold.