The spokesman of German Chancellor Angela Merkel says if reports that Washington spied on its European allies are true, the behavior is "unacceptable."
Steffen Seibert also said that Merkel was "alienated" by the reported eavesdropping.
Germany's reaction came as the European Commission also expressed its displeasure over Washington's reported espionage activities.
"[This is] disturbing news," spokeswoman Pia Ahrenkilde Hansen said in Brussels. "If proven true, they demand full clarification. And as soon as the media reports about alleged spying and eavesdropping on EU premises and delegations were made known, the [European] Commission asked the European External Action Service to immediately raise the matter with the U.S. authorities in Washington, D.C., and in Brussels to verify the veracity of these reports."
On July 1, the British daily "The Guardian" cited leaks by fugitive U.S. intelligence analyst Edward Snowden indicating Washington spied on 38 embassies and representative offices of its European and non-European allies, including France, Italy, Greece, Japan, and Turkey.
Earlier, Germany's "Der Spiegel" magazine reported the EU's offices in Washington, New York, and Brussels were targeted and communications were monitored in Germany.
The German magazine said some countries, including Britain and Canada, were placed in a special group excluded from the spying program.
U.S. Secretary of State John Kerry addressed the spying allegations at a meeting of Association of Southeast Asian Nations (ASEAN) foreign ministers in Brunei.
"I will say that every country in the world that is engaged in international affairs of national security undertakes lots of activities to protect its national security," he said, "and all kinds of information contributes to that. And all I know is that that is not unusual for lots of nations. But beyond that, I am not going to comment any further until I have all of the facts and find out precisely what the situation is."
He has to stop his work directed at hurting our American partners, as strange as it sounds coming from me.
French President Francois Hollande told journalists that "enough elements have already been gathered for us to ask for explanations." He added, "We ask that this [spying] immediately stop."
The "Der Spiegel" report said a document leaked by Snowden showed that the EU and French missions at the United Nations were among those targeted.
In Geneva, UN Secretary-General Ban Ki-moon objected to the reported U.S. targeting of other governments’ missions to the United Nations.
"The inviolability of diplomatic missions, including the United Nations and other international organizations, whose functions are protected by relevant international conventions, like the Vienna Convention, I think that is a well-established international law," Ban said. "Therefore, [UN] member states are expected to act accordingly to protect the inviolability of diplomatic missions."
Snowden, who leaked the details of U.S. surveillance programs, faces espionage charges in the United States.
He was last seen disembarking from a plane at Moscow’s Sheremetyevo Airport on June 23. He is believed to still be in the transit area there. Moscow has indicated it would not expel him back to the United States.
"Russia never gives up anyone to anybody and is not planning to. And nobody ever gave anyone up to us," Russian President Vladimir Putin said on July 1.
Putin said Snowden could remain in Russia but must meet at least one condition.
"He has to stop his work directed at hurting our American partners," Putin said, "as strange as it sounds coming from me."
Putin denied that Snowden is cooperating with Russian intelligence or security services and said Snowden considers himself a human rights activist.
Ecuador has been mentioned as a possible final destination for Snowden. Ecuadorean President Rafael Correa said on June 30 that his country cannot consider any asylum request until Snowden reaches Ecuador or an Ecuadorean Embassy.
With reporting by Reuters and AFP