On arrival at an EU summit in Brussels Mrs Merkel said "we need trust between allies and partners, and such trust needs to be restored".
She said she had given that message to US President Barack Obama when they spoke on Wednesday.
Other EU leaders also voiced concern about the scale of US surveillance.
The spying row threatens to overshadow EU talks on economic growth and migration to the EU. Mrs Merkel has demanded a "complete explanation" of the claims, which came out in the German media.
She grew up in former communist East Germany, where secret police surveillance was pervasive.
Her delegation in Brussels confirmed she had met briefly to discuss the issue with France's President Francois Hollande, who has expressed alarm at reports that millions of French calls have been monitored by the US.
There is concern that the furore could jeopardise EU-US talks on reaching a major free trade deal. The head of Germany's Social Democrats (SPD), Sigmar Gabriel, said such a deal was hard to imagine if the US had infringed citizens' privacy. The SPD is in coalition talks with Chancellor Merkel. (+ video) » | Thursday, October 24, 2013
