U.S. Steel CEO David Burritt said Tuesday he was confident Nippon Steel's $14.9 billion bid for his company would "close on its merits," despite political opposition and concerns raised in a national security review.

Burritt, speaking at the Detroit Economic Club, described the review process as "very robust" but added, "we trust the process, we respect the process."

The Committee on Foreign Investment in the United States, which has been reviewing the deal, appeared poised to block it on Aug. 31, when it sent the companies a 17-page letter exclusively reported by Reuters. The letter alleged that the transaction posed a risk to national security by threatening the steel supply chain for critical U.S. industries.

The companies countered in a 100-page letter, also exclusively reported by Reuters, that the deal would enhance U.S. national security by allowing a company from an allied nation to make a much-needed investment in a struggling U.S. firm in a critical sector.

CFIUS did not immediately respond to a request for comment.

Nippon's planned acquisition of the U.S. steelmaker also faces opposition from powerful Democrats and Republicans. U.S. Vice President and Democratic presidential candidate Kamala Harris has said she wants U.S. Steel to remain "American-owned and operated," while her Republican rival Donald Trump has pledged to block the deal if elected.