The president of Nippon Steel says he cannot be optimistic about its takeover of US Steel due to opposition from the United Steelworkers union, or USW.

The major Japanese and US steelmakers agreed on the deal in December last year.

The US Committee on Foreign Investment, which examines acquisition plans, has extended a period for reviewing the Nippon Steel's plan to acquire US Steel.

Media reports say the committee may postpone its decision on the takeover until after the US presidential election in November.

On Thursday, Nippon Steel president Imai Tadashi, who also heads the Japan Iron and Steel Federation, told reporters that he does not think it an optimistic development that the deal is now being reviewed for an extended period.

Imai said that he is still determined to complete the acquisition by the end of the year.

He also said that the deal has been drawing a lot of attention in the run-up to the US presidential election because it involves the USW, which represents 850,000 steelworkers.

Imai added that his company will place a focus on dialogue with the USW and do all it can.

He urged the union to respond to Nippon Steel's call for negotiations.