The uproar comes after Denmark’s public broadcaster reported on Sunday that the country’s intelligence service helped the U.S. eavesdrop on European officials almost a decade ago.
NBC News has not verified the report, which has thrust the issue back into the spotlight years after it first led to a diplomatic rift between Washington and Berlin.
French President Emmanuel Macron said on Monday that any American eavesdropping on European countries would not be “acceptable amongst allies.”
Macron said he was “attached to the bond of trust that unites Europeans and Americans,” asserting that “there is no room for suspicion between us.”
Merkel said she could only echo Macron's stance, noting that the allegations related to events several years ago but that they were serious if accurate.
Officials from Sweden and Norway joined the criticism and said they wanted Denmark to explain its alleged involvement.
“We want the cards on the table,’ said Swedish Defense Minister Peter Hulqvist, adding it was “unacceptable to eavesdrop on allies.”
What are the allegations?
The Danish broadcaster DR reported Sunday that the Danish Defense Intelligence Service, known in Denmark by its acronym FE, in 2014 conducted an internal investigation which concluded that the U.S. had used cooperation with the Danes to spy against Denmark and neighboring countries.
The National Security Agency (NSA) is alleged to have used Danish resources to spy on senior officials in Germany, France, Sweden and Norway from 2012 to 2014, in an initiative codenamed “Operation Dunhammer.”
NBC News has not verified the report.
Approached for comment, a spokesperson for the State Department referred NBC News to the NSA, while an NSA spokesperson said the intelligence agency has “no comment” on the allegations.
NBC News has contacted FE and the French government for comment.
A spokesperson for the German government referred NBC News to Merkel’s comments, saying that officials had nothing else to add.
In a statement shared with NBC News, Defence Minister Trine Bramsen said the Danish government “can and will not comment on speculation in the media concerning our intelligence service.”
However, she said: “The position of the Danish government is clear — systematic targeting against our close allied partners is unacceptable.”
“Clearly, that is a well-established principle that Danish authorities adhere to.”
Bramsen was appointed to her role in 2019, years after the eavesdropping is alleged to have been carried out during the administration of former President Barack Obama.
Obama's tenure in the White House saw an otherwise warm relationship with Berlin damaged by reports in 2013 that the NSA was listening in on German government phone lines, including Merkel’s.
Those allegations first came to light in reports leaked by whistleblower Edward Snowden, who reacted to the latest report with a sarcastic tweet in Danish: “Oh, why didn’t anyone warn us?"
Obama apologized to Merkel at the time and also said he knew nothing about the alleged spying and would have blocked it if he did.
Now the renewed spotlight on the issue could create a headache for President Joe Biden, who is set to travel to Europe later this month for the Group of Seven summit of world leaders in Cornwall, U.K.
Biden has vowed to “repair” U.S. alliances and re-engage with the world after four years of President Donald Trump’s “America First” doctrine.
On his first day in office, Biden signed a string of orders solidifying that commitment, including rejoining the Paris climate agreement and the World Health Organization.
The trip to Europe will be Biden’s first major opportunity to outline his foreign policy vision on the international stage, and a chance to convince his counterparts that America can be a trusted partner again.