Senior administration officials are meeting with German intelligence officials at the White House on Wednesday to discuss allegations that the National Security Agency tapped Chancellor Angela Merkel's mobile phone.

Germany has expressed outrage over the alleged surveillance, and the United States has scrambled to soothe tensions with its European ally.

Last week, President Obama and Merkel spoke by phone, with the president assuring the German chancellor that the United States was not and would not monitor her communications.

But that left open the question of whether the U.S. had done so in the past, and provoked a fiery response from the German leader.

Merkel said that "spying among friends is not at all acceptable against anyone," and dispatched a team of her top intelligence officials to the U.S. to investigate the extent of the surveillance practices.

"It's not just about me but about every German citizen. We need to have trust in our allies and partners, and this trust must now be established once again," she said, according to Reuters.

National Security Advisor Susan Rice, chief counterterrosism adviser Lisa Monaco, Director of National Intelligence James Clapper and deputy NSA director John Inglis are expected to attend the Wednesday's meeting.

Germany's delegation includes Christoph Heusgen, Merkel's foreign policy adviser, and Guenter Heiss, the German Chancellery Intelligence Coordinator.

"In their recent telephone conversation, President Obama and Chancellor Merkel agreed to intensify further the cooperation between U.S. and German intelligence services," National Security Council spokesperson Caitlin Hayden said, characterizing Wednesday's meeting as "a part of that dialogue."

But while the White House is looking to smooth out diplomatic concerns over its intelligence activities, Clapper defended the practice of surveilling foreign leaders when he testified before Congress on Tuesday.

Clapper said that attempting to determine the intentions of foreign leaders was a "fundamental given" in the intelligence world, and that the U.S. "absolutely" believed allies were spying on American leaders.

A spokesperson for Senate Intelligence Committee Chairwoman Dianne Feinstein (D-Calif.) said on Monday that the White House has decided to halt surveillance on foreign leaders going forward, although the administration has so far refused to confirm that.

White House press secretary Jay Carney on Tuesday acknowledged that the White House consulted "regularly" with Feinstein, but refused to confirm whether a decision to cut surveillance of allied leaders had been made.

Carney reiterated that the U.S. planned a "review of our activities around the world," but said the administration was "not going to discuss the details or the outcomes until it's completed."