Nippon Steel Vice Chairman Takahiro Mori said on Tuesday the Japanese company remains committed to talks with the United Steelworkers (USW) labor union over its bid to acquire U.S. Steel.

Separately, Nippon Steel said it would sell its entire stake in South Korean steelmaker Posco Holdings, worth about $820 million based on Monday's closing price in Seoul, amid reports it is looking to offload assets ahead of the U.S. Steel takeover. Nippon Steel said in a statement to the Tokyo exchange it will sell 2.9 million Posco shares in an effort to "improve asset efficiency."

Mori, the key negotiator of the $14.9 billion buyout deal, said USW President David McCall "has not seriously considered any of the proposals that we have presented" in a letter to the U.S. Steel employees.