Chancellor Angela Merkel has defended her decision to phase out nuclear energy, even though it has made it harder for Germany to wean its economy off fossil fuels.

In an interview, the outgoing chancellor also said she was opposed to any plans by the European Union to label nuclear power as "sustainable."

"It's true, of course, that we now face the very ambitious and challenging task of completing the energy transition while phasing out coal and nuclear power," said Merkel, who will step down once a new government is sworn in following an election in September.