UPDATE 1-Liberty Steel's funding plan for Thyssenkrupp lacks clarity -IG Metall

* Liberty Steel plan not backed by sustainable concept-union

* Spin-off can be interesting if it secures parent group

* Thyssenkrupp AGM takes place on Feb. 5 (Adds additional comments)

DUESSELDORF, Feb 4 (Reuters) - A bid by Britain’s Liberty Steel for the steel division of Germany’s Thyssenkrupp still lacks clarity on financing, a leader for the powerful IG Metall union said.

“Liberty has an idea. But it is unclear how it will be funded,” IG Metall’s North Rhine-Westphalian regional leader Knut Giesler told Reuters ahead of Thyssenkrupp’s annual general meeting on Friday.

“It hasn’t been proven yet that it’s a sustainable concept.”

Liberty Steel last month submitted what it called a firmed up bid for the division, with sources saying the group had secured significant financial leeway to fund the transaction.

In addition, Thyssenkrupp is also exploring a spin-off of the steel unit, while a third option could entail keeping the business and developing it under the roof of the parent group.

“A spin-off idea can be interesting, if it secures the whole company with 95,000 employees,” Giesler said, adding IG Metall would benchmark all options against its key demands.

“Our red lines are known. We have a collective bargaining agreement. The commitments made on securing jobs, keeping sites and investments must be guaranteed.” (Writing by Christoph Steitz; Editing by Madeline Chambers)