Heinrich von Pierer, a former boss of electronics giant Siemens who would shape economy strategy for Merkel's Christian Union if it wins on September 18, sparked controversy by calling for Germany's nuclear energy programme to be extended over a 60-year period.

That is almost twice as long as the 32-year target for phasing out nuclear power stations set by the current coalition government of the Greens and Chancellor Gerhard Schroeder's Social Democrats.

Environment Minister Juergen Trittin, a member of the Greens, said von Pierer was "acting like a lobbyist for nuclear energy companies".

Instead of coming up with an innovative energy strategy, von Pierer was "promoting the supposed merits of old and inefficient technology", Trittin said.

Greens co-leader Claudia Roth meanwhile accused the Christian Union of being "ignorant of the dangers of nuclear technology".

The Christian Union -- the Christian Democratic Union (CDU) and its Bavarian sister party the Christian Social Union -- is pledging in its election manifesto to reverse the phase-out of nuclear energy, but Merkel had until now called for the programme to be extended only over 40 years.

Polls show the Christian Union holds a clear lead over the Social Democrats.

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