Furious German officials said Wednesday that U.S. intelligence agencies may have been monitoring German Chancellor Angela Merkel's cellphone, creating a fresh diplomatic headache for President Barack Obama after a week in which other close allies condemned his administration over allegations of other spying misdeeds.

The German leader called Obama on Wednesday about the issue, forcing him to assure a European leader for the second time this week that the United States had not overstepped boundaries in its eavesdropping programs.

Obama told Merkel, an ally who has been upset since the extent of the U.S. surveillance programs was disclosed several months ago, that the United States is not eavesdropping on her telephone calls, the White House said Wednesday. Reports in Germany raised fears that such spying was taking place.