Germany's Green party announced on Tuesday that it would no longer continue coalition talks with Angela Merkel's CDU and will most likely opt for four years in political opposition instead.

After their second round of talks with the CDU, Green party leaders said there was no resilient basis for entering a coalition with the conservatives. The areas where the two parties could not find sufficient common ground included tax rises, the introduction of a minimum wage and Europe, they said.

Ironically, the Greens and the CDU also disagreed over the future of Germany's Energiewende, or nuclear phase-out; the very policy area that had led to speculation about a CDU-Green coalition in the first place. In 2011 Merkel announced the gradual closure of all German nuclear power stations by 2022 – something the Greens had been calling for for some time.

"On the question of the nuclear phase-out, which is a key challenge for us, we twice tried to get a more concrete answer, but we failed to reach an agreement," said the Greens' vice-president, Claudia Roth. Merkel's answers had been "diffuse, not very concrete".

The announcement now increases the pressure on the next round of coalition talks between Merkel's party and the Social Democrats. The SPD is still seen by many as close to the coal industry but shares considerable common ground with Merkel on her other big challenge for the next four years: the future of the eurozone.

Should coalition talks with the SPD fail nonetheless, a coalition between the SPD, the Greens and the leftwing Die Linke, or even a return to the polling booths, is not out of the question.

On Tuesday night it appeared even the Greens were reluctant to rule themselves out: "The door isn't nailed shut with the kind of long nails that you can't pull out again," said the Green co-chairman Cem Özdemir.