"The recent destabilizing and defiant actions by North Korea, in clear violation of numerous U.N. Security Council resolutions, must be met with strength and resolve," said the letter, written by Reps. Peter Roskam (R-IL), Ami Bera (D-CA), Gerry Connolly (D-VA) and Mike Kelly (R-PA).

"At the same time, we must conduct our foreign and national security policy in a manner that eliminates the North Korean nuclear threat while averting war on the Korean Peninsula," it said. "To this end, it is pivotal we uphold our commitments to the Republic of Korea -- a US treaty ally -- and endeavor through our alliance to maintain peace and prosperity on the Peninsula, in the region, and beyond."

The Korea-US free trade agreement, known as KORUS, has achieved its goal of expanding bilateral trade, and its shortcomings must be addressed through modifications, the lawmakers noted.

"We must recognize that we cannot jeopardize our alliance through these negotiations or by unilaterally withdrawing from KORUS at this precarious moment," they said, referring to the bilateral talks that got under way last month.

"Trade and security go hand in hand," the letter added. "Any negotiations must factor in the importance of strengthening our relationship with South Korea and maintaining a united front against North Korea." (Yonhap)