(CNN) -- Germany has information that the United States might have monitored Chancellor Angela Merkel's cell phone, a German government spokesman said Wednesday.
"We have immediately sent a question to our American partners and have asked for immediate and wide-ranging clarification," spokesman Steffen Seibert said in a written statement.
Both governments said that Merkel spoke about the issue with President Barack Obama during a phone call Wednesday.
Obama told her that the United States "is not monitoring and will not monitor" her communications, White House spokesman Jay Carney said.
Merkel made it clear that, if the information about the U.S. having monitored her phone were true, it would be "completely unacceptable," Seibert said.
"Close friends and partners, such as Germany and the USA have been for decades, cannot have monitoring of communication of a head of government," Seibert said. "This would be a grave breach of trust. Such practices have to stop immediately."
Germany and other nations expressed concerns about alleged U.S. spying after former National Security Agency contractor Edward Snowden leaked classified information about American surveillance programs.
German news magazine Der Spiegel reported in June that classified leaks from Snowden detailed how the agency bugged EU offices in Washington and New York as well as conducting an "electronic eavesdropping operation" that tapped into an EU building in Brussels.
Merkel spoke with Obama by phone in July about allegations that the United States was conducting surveillance on its European allies.
CNN's Stephanie Halasz contributed to this report.