General Motors and the German government played down hopes on Friday of a quick decision on the sale of the carmaker's Opel unit, and Berlin reiterated its support for Canadian bidder Magna .

German Chancellor Angela Merkel, speaking at a news conference with Russian President Dmitry Medvedev in the Black Sea resort of Sochi, said talks on Opel's future had reached a decisive phase but reaching a quick deal would be tough.

Such negotiations are sometimes difficult and you need patience, Merkel said. Therefore I am not able to say today when they will be concluded -- we would like this to be as soon as possible.

She reiterated her support for a bid from Magna, an auto parts group whose bid is backed by Russian investors.

GM's top negotiator for the sale, John Smith, said his company still needed to compare a new offer it received from Magna on Thursday with an attractive proposal from rival bidder, Belgium-based financial investor RHJ .

Although Germany has made clear it is up to GM to decide the victor in the bidding showdown, Berlin is being asked to cough up billions of euros in finance guarantees to the winner and so it wields considerable influence.

Some GM executives are believed to favor the RHJ offer over Magna's but Berlin, the four German states where Opel has plants and Opel unions all favor Magna.

GM's Smith said on a blog that the U.S. carmaker was awaiting input about what state aid it could expect from European countries that host Opel plants before management presents its findings to GM's board of directors next week.

After the GM board makes its recommendation, the Opel Trust Board will be asked for its approval. So, there is more to consider, and more to do, before an agreement for Opel is reached, Smith said.

A spokesman for the German Economy Ministry confirmed that the government's Opel task force would meet on Monday to examine the offers from Magna and RHJ, but was vague about when decisions could come.

It is primarily up to GM to evaluate the offers, Steffen Moritz said at a news conference. We will look at the contracts but I can't say when this process will be finalized.

Hopes for a swift deal between Magna and GM grew on Thursday when the Canadian company said that it had reached an agreement in principle with GM management over a contract to buy 55 percent of Opel, together with Russian partner Sberbank .

But Smith said GM had not reached an agreement with Magna .

Merkel said GM, Berlin, the state governments and other European governments would need to come to a decision together.

No one can decide anything without the other, so there is a need to come to an agreement, she said.

(Additional Reporting by Brian Rohan, Sarah Marsh and Dave Graham in Berlin; Editing by Simon Jessop)