UPDATE 1-Germany's Postbank nears sale-source

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DUESSELDORF, Germany, June 24 (Reuters) - Germany's biggest retail bank, Deutsche Postbank (DPBGn.DE), is edging closer towards a sale, a source with direct knowledge of the matter said on Tuesday.

Postbank had already been put up for sale by its owner, Deutsche Post (DPWGn.DE), sources have told Reuters.

A source told Reuters on Tuesday that Post was in advanced talks with buyers from Germany and abroad, denting market talk the auction may be postponed.

"Post wants to step on the gas," the source said.

Deutsche Bank (DBKGn.DE) has flagged its interest, as have Allianz (ALVG.DE) and Commerzbank (CBKG.DE), which are pitching together and hope to swallow Postbank into a newly created group that would include Allianz's Dresdner Bank.

The source said such a three-way deal was "not a must", noting a deal between Commerzbank and Dresdner would have to come first.

A Deutsche Post spokesman said only that the process of exploring a Postbank sale was still under way. Allianz and Commerzbank declined comment.

Signals pointed to a quick sale of Postbank after sources earlier told Reuters that owner Post had received expressions of interest for Postbank well above its market value of nearly 10 billion euros ($15.56 billion).