The deadline, which sources said was due to expire later on Wednesday, will be extended by eight working days, Thyssenkrupp said. This will move the overall deadline for a decision to May 13 from April 29, the Commission said on its website.

"In the ongoing merger control proceedings the deadline to submit a proposal, through which Thyssenkrupp and Tata Steel will address the Commission's concerns, is imminent," a spokesman for Thyssenkrupp said in e-mailed comments.

"To adequately draw up the proposal the partners have agreed to apply for an extension by 8 working days as part of the constructive dialogue with the Commission."

Thyssenkrupp confirmed it remains confident that the transaction, which will create Europe's second-largest steelmaker after ArcelorMittal, can be completed in the spring.

Sources told Reuters this month that the companies are unlikely to make far-reaching concessions that will jeopardise the economic and strategic rationale of the deal.

(Reporting by Christoph Steitz; editing by Thomas Seythal and Alexander Smith)