(CNN) -- The House Intelligence Committee is set to question U.S. spy chiefs about accusations that the National Security Agency has tapped not only the phone calls of millions of Americans, but those of top U.S. allies.
Among those on the hot seat will be Director of National Intelligence James Clapper.
Germany's interior minister said Monday that his country's confidence in the United States is shaken, amid claims the NSA monitored Chancellor Angela Merkel's cell phone.
"If the Americans intercepted cell phones in Germany, they broke German law on German soil," Interior Minister Hans-Peter Friedrich told the Bild am Sonntag newspaper, adding that he wants "complete information on all accusations."
"The confidence in our ally, U.S.A., is shaken," Friedrich said, according to Bild am Sonntag.
Citing an unnamed intelligence officer, the German newspaper also reported Sunday that U.S. President Barack Obama learned about the NSA operation targeting Merkel from agency chief Gen. Keith Alexander in 2010 and allowed it to continue -- a claim the NSA denied.
"Gen. Alexander did not discuss with President Obama in 2010 an alleged foreign intelligence operation involving German Chancellor Merkel, nor has he ever discussed alleged operations involving Chancellor Merkel," NSA spokeswoman Vanee' Vines told CNN.
German magazine Der Spiegel, meanwhile, reported that Obama told Merkel he would have stopped it from happening if he had known about it.
Such reassurances appear to have done little to quell outrage from German officials about the alleged espionage, which was reported last week by Der Spiegel.
The magazine's report, which cites a secret U.S. intelligence file, claimed Merkel's phone had been monitored for more than 10 years, stretching back before her current post.
It's the latest in a series of spying allegations that stem from disclosures given to news organizations by Edward Snowden, the former NSA contractor who describes himself as a whistle-blower.
The same database indicated the United States was spying on others in Berlin's political district, at least until Obama visited Berlin this year, Der Spiegel reported.
Asked about the assertions, U.S. National Security Council spokeswoman Caitlin Hayden said her agency does not "comment publicly on every specific intelligence activity."
"And, as a matter of policy, we have made clear that the United States gathers foreign intelligence of the type gathered by all nations," said Hayden, echoing comments she and others have made in recent days.
On Monday, the Obama administration declassified a new batch of NSA documents, many of which deal with the effort to inform members of Congress about NSA programs that collect call data on nearly every U.S. telephone user.
Most of the documents, released by Clapper, date to 2009, when the administration was pushing lawmakers to reauthorize sections of the Patriot Act that were set to expire.
One document from 2011 notifies the House and Senate intelligence and judiciary committees of the NSA's testing in 2010-11 of a program to collect cell phone tower data that could track mobile phone users. The NSA this month acknowledged it tested such collection but discontinued it.
The document released Monday said the Justice Department prepared a memorandum authorizing the program, which the document said fell legally within guidelines of another program under Section 215 of the Patriot Act.
"It appears that the NSA embarked on an effort to track Americans' movements in bulk without even seeking explicit approval from the FISA court beforehand," said Alex Abdo, an attorney with the American Civil Liberties Union's National Security Project. "That is hardly the robust judicial oversight the government has repeatedly promised. To the contrary, it is further evidence that Congress should rein in NSA spying on innocent Americans and put an end to mass collection of our private information."
The Foreign Intelligence Surveillance Court, or FISA court, grants or refuses surveillance rights requests from U.S. government agencies.
Another document, also from 2011, is the NSA's notification to the Senate and House judiciary committees about a program carried out under Section 501 of the Foreign Intelligence Surveillance Act to collect mobile phone data, known as metadata, that includes the numbers called and date, time and length of calls.
The collection began in 2006 and matched the NSA's collection of land line telephone data.
Most of the newly declassified documents describe the aggressive push by the NSA, FBI and the Justice Department for lawmakers to save the bulk telephone data collection effort, known as the 215 program, because it was important for their efforts to thwart terrorist threats.
At the same time, lawmakers were urged not to discuss the classified program for fear it would hurt national security, the documents say.
Earlier this year, after Snowden released thousands of classified documents, including court orders detailing the 215 bulk data program, many lawmakers said they were shocked about the extent of the program.