German Economy Minister Karl-Theodor zu Guttenberg said on Sunday he hoped General Motors and the U.S. government would help answer remaining questions on a plan to save German unit Opel.

I hope GM and the U.S. government will be ready to shed some light on the issue, Guttenberg told Reuters.

GM Europe submitted a rescue plan for Opel last month under which the German unit and GM's UK-based Vauxhall unit would be partly spun off into a new subsidiary. It said the independent unit would need 3.3 billion euros in state aid.

German Chancellor Angela Merkel has said the German state would only grant aid to companies such as Opel if it would secure their future and not just evaporate without any effect.

Merkel also has said that any decision on German government help for Opel depended on decisions the U.S. administration made on aid to the carmaker's parent, General Motors.

The Obama administration's auto task force faces a March 31 deadline to determine whether GM and Chrysler can be commercially viable and deserving of more government aid.

They received a $17.4 billion bailout in December and have asked for an additional $22 billion.

In a radio interview broadcast on Sunday, Merkel said Economy Minister Guttenberg had to assess in his talks this week to what extent General Motors could grant Opel more liberties.

If we then manage to find an investor who makes clear he sees positive prospects for Opel in a European network, we will be able to see whether we can help with normal government instruments, such as guarantees, she told Deutschlandfunk.

Differences over Opel have emerged within Germany's grand coalition government of Merkel's party, the conservative Christian Democrats (CDU), and the Social Democratic Party (SPD), with SPD officials saying the CDU risked jeopardizing German industry if they failed to help Opel.

But members of the CDU have also called for a more pro-active stance on Opel.

Roland Koch, the state premier of the western state of Hesse where Opel has a large production site, on Saturday expressed a positive view on the rescue plan the company had provided.

(Reporting by Hans-Edzard Busemann; writing by Kerstin Gehmlich; editing by Karen Foster)