A clear majority of Americans say it's "unacceptable" for the United States to monitor the phones of leaders of countries that are allied with the United States, according to a new poll.

The Pew Research Center poll shows 56 percent say it's unacceptable, while 36 percent say it's acceptable.

Opposition is at least 53 percent among Republicans, Democrats and independents -- suggesting universal condemnation of the practice.

Recent news reports say that the United States monitored the phone of German Chancellor Angela Merkel and dozens of other world leaders. The White House has denied the U.S. intelligence is currently monitoring Merkel's phone or that it will do so in the future, but has notably declined to say whether it has done so in the past.

The spying has sparked outrage in Europe. German officials are investigating and say the episode could reduce cooperation with the United States on counterterrorism.