Merkel's comments came after a senior U.S. official argued that nuclear power should be used to stem emissions.
"A country that has the capability to responsibly use nuclear energy in my view has a responsibility to do so, if we want to get serious about not just cutting greenhouse gas emissions, but also improving public health through reduced air pollution," said James Connaughton, chairman of the White House Council on Environmental Quality.
Asked if that was a dig at Germany, since Merkel is sticking to her predecessor's plan to phase out Germany's 17 nuclear power plants in the coming years, Connaughton did not respond directly.
Merkel countered: "I don't think that climate protection is decided by the question of nuclear energy alone."
Taking steps to tackle global warming is high on the agenda for the G-8 meeting, which brings together leaders from the U.S., Germany, Japan, France, Italy, Canada, Russia and Britain.
Germany's governing coalition is deeply divided over nuclear energy.
The conservative Merkel's "grand coalition" government has stuck with its center-left predecessor's decision to phase out Germany's nuclear power plants — but the plan has caused repeated political friction, particularly with an election looming next year.
Merkel made clear that she personally opposes switching off nuclear power plants early. However, she said that "we must above all go down the new paths," such as using more renewable energy and improving energy efficiency, in combating climate change.
"The decision that many countries count on nuclear power is OK," Merkel said. "But to say that the future for climate change and careful use of energy can be solved by that alone — I don't see it that way."
Merkel's center-left coalition partners, the Social Democrats, have fiercely defended the shutdown plan agreed by the previous government, which they led in a coalition with the Greens.
In Berlin on Monday, Social Democratic general secretary Hubertus Heil said that "there is no such thing as safe nuclear energy."
(Source: International Herald Tribune)