March 15 (Reuters) - U.S. Steel Corp said in a regulatory filing on Friday that the acquisition by Nippon Steel is expected to close later this year.

The filing with exchanges comes at a time when the Japanese firm's $14.9-billion deal to buy the iconic 122-year-old U.S. steelmaker faces heightened scrutiny due to national security concerns.

U.S. President Joe Biden on Thursday expressed explicit opposition to the deal and said U.S. Steel must remain a domestically owned American firm. (Reporting by Pratyush Thakur in Bengaluru; Editing by Shweta Agarwal and Shounak Dasgupta)