Cleveland-Cliffs Inc. said it made a bid to purchase United States Steel Corp. in a cash and stock deal as it looks to create one of the world’s largest steelmakers.

US Steel on Sunday rejected the offer as being “unreasonable,” Cleveland-Cliffs said.

Cleveland-Cliffs offered to pay $17.50 in cash and 1.023 of its shares for each US Steel stock, the company said in a statement Sunday. That implies a value of $32.53 per share as of Friday’s close, a 43% premium to US Steel’s last closing price of $22.72.

The announcement comes hours after US Steel said it began a formal review of strategic alternatives after receiving “multiple unsolicited” proposals, ranging from acquisition of certain production assets to offers for the whole company.