BERLIN, March 17 (Reuters) - The premier of the German state of Hesse on Tuesday called on Italy's UniCredit to submit a concrete offer for the German lender Commerzbank and to clarify its objectives.

"I support the clear expectation for UniCredit to put a concrete offer on the table," Boris Rhein, whose state includes the financial centre Frankfurt where Commerzbank is headquartered, told Reuters.

UniCredit has increased pressure on Commerzbank to accept merger talks with a low-ball bid to raise its stake in Commerzbank above 30%.

Commerzbank Bettina Orlopp on Tuesday called the offer "very low" and complained Unicredit was not informing it about its vision for a tie-up, underscoring Commerzbank's long-held reluctance about any takeover deal.

Germany's federal government has opposed a hostile takeover while Rhein's state government has said Frankfurt's position as Europe's leading financial centre must be strengthened.