"One cannot conduct surveillance and spy on one's friends," Maurer told Swiss public broadcaster SRF.
"That is how you disrupt confidence between states," he said.
"Even if you are big and powerful, you cannot sit on those who are smaller than you and bug their phones," he said.
"In the end, this will not strengthen the United States.
"Quite the opposite, it weakens the country."
Maurer's comments came amid mounting global outrage over reports of widespread US spying on foreign citizens, as well as on a number of world leaders, including German Chancellor Angela Merkel.
"Freedom is a fundamental value," Maurer said.
"To spy on either politicians or citizens is not ok," he said.
"It is not part of our culture,"
Switzerland had no immediate plans to react officially to the allegations that Merkel's mobile phone had been tapped, Maurer said.
"We are still studying what may have happened here and how we should react."