The White House on Monday defended the U.S. National Security Agency (NSA) following further media exposures of its alleged spying on America's European allies and strong criticism from world leaders.

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Demonstrators hold placards and banners to protest against government surveillance in Washington D.C., capital of the United Sates, on Oct. 26, 2013. Hundreds gathered here on Saturday demanding the U.S. Congress to investigate the U.S. National Security Agency (NSA) mass surveillance programs, ban blanket surveillance of telephone and Internet activity, and pursue accountability for any officials who misled lawmakers and the American people.

U.S. President Barack Obama has "full confidence" in NSA Director Keith Alexander and the agency's rank-and-file who work on behalf of Americans and its allies and "keeping them safe," White House spokesman Jay Carney said at a daily press briefing.

Carney argued that there has been "extraordinary" changes in the past decade since 9/11 that has affected the whole world in the way of transmitting and gathering information.

"If we're going to keep our citizens and our allies safe, we have to continue to stay ahead of these changes, and that's what our intelligence community has been doing extraordinarily well," he said. "These capabilities are part of the reason we've been able to foil numerous terrorist plots and adapt to a post-9/11 security environment."

Carney dodged a question about whether Obama knew about the alleged surveillance of German Chancellor Angela Merkel before the media revelation, only saying that the president made clear in his phone conversation with Merkel last week that the United States does not and will not monitor her communications.

But he did acknowledge the "tensions these disclosures have caused" with U.S. allies.

Carney said an entire review of the surveillance programs being led by the White House will be completed by the end of the year.

The defense of the NSA comes amid outrage and criticism from American allies in Europe over media reports that U.S. intelligence agencies have monitored the emails and phone calls of Merkel and 70 millions of phone calls between French citizens. The latest report on Monday alleged that the NSA also spied on more than 60 million phone calls in Spain.

Source: Xinhuanet