Chancellor Angela Merkel placed much of the blame for her party's poor performance in a weekend election on Germany's discussion about nuclear energy, and said Monday she hopes "quick and clear decisions" on its future will defuse the issue.

Merkel's conservative Christian Democrats slipped behind the environmentalist opposition Greens into third place in Bremen, Germany's smallest state, in Sunday's regional election. It was their worst showing there since 1959.

In March, the Christian Democrats lost a traditional heartland, the southwestern state of Baden-Wuerttemberg, to a Green-led center-left coalition.

Merkel said both votes were marked by Germany's discussion over nuclear energy.

Japan's nuclear disaster has tipped atomic power over the line from unpopular to politically toxic in Germany. It prompted Merkel to freeze a recent decision to extend the life of the nation's 17 nuclear reactors, which a previous government had decided to shut by 2021.

Merkel's center-right coalition is due to decide in the coming weeks on how to proceed with nuclear energy and move to renewable sources faster than previously planned. The chancellor pledged "quick and clear decisions in the area of energy policy."

In recent elections, "we have seen very high mobilization among those who are interested in energy policy questions — particularly Green voters — and that's why it is important that we decide on this issue," she said.

By the time Berlin votes in September, in the last of seven state elections this year, energy policy will be decided and "the issues that arise ... will be different," she insisted.

Bremen is traditionally a stronghold of the opposition center-left Social Democrats, who will continue to govern the state with the Greens. Merkel said her party also was hurt by having no realistic chance of power there.

Merkel's governing coalition with the pro-business Free Democrats, who failed to win seats in Bremen's state legislature Sunday, has been plagued by internal squabbling since it took power in late 2009 and it is struggling in polls.

"It is our job — we are not even in the middle of the parliamentary term — to lead the ... coalition to success," the chancellor said.

Greens co-leader Claudia Roth described Sunday's result as "a clear signal to the national government ... to exit nuclear energy as soon as possible."

The election, she said, was a "further step" toward defeating Merkel's coalition in Germany's 2013 national election.