Besides the U.S. National Security Agency, Merkel's phone was monitored by the British, Russian, Chinese and North Korean surveillance agencies, weekly news magazine Focus reported, citing an unnamed German security official.
A German government spokeswoman declined to comment to The Wall Street Journal on the report.
Documents leaked by former NSA contractor Edward Snowden have revealed the U.S. spy agency monitored Merkel's phone for a decade starting in 2002. Merkel was elected chancellor in 2005.
U.S. Senate Intelligence Committee Chairwoman Dianne Feinstein, D-Calif., later confirmed Merkel's phone was tapped.
She added she did "not believe the United States should be collecting phone calls or emails of friendly presidents and prime ministers."
Focus magazine also said foreign intelligence agencies tried more than 100 times last year to recruit German politicians, civil servants, military personnel and other people, including scientists, to be informants.
Russia is particularly active in Germany, the magazine said.
German intelligence officials said last week they would fortify their countersurveillance efforts in response to the NSA spying revelations.