U.S. Democratic presidential candidate Joe Biden sought Korean-American support on Friday, thanking them for their contributions and promising to strengthen the U.S. alliance with South Korea. 

In a letter to Seoul-based Yonhap News Agency, Biden vowed not to "extort" South Korea with "reckless threats" to remove American troops from the Korean Peninsula.

He also vowed to engage in principled diplomacy and keep pressing toward a denuclearized North Korea and a unified Korean Peninsula.

The allies have been deadlocked in negotiations to renew their defense cost-sharing agreement after the Trump administration demanded Seoul drastically increase its contribution initially by fivefold, later by 50 percent. 

Biden has criticized Trump for only serving to justify the North Korean regime through his "top-down" approach towards denuclearization.

Biden also highlighted the alliance "forged in blood," saying South Korea is a strong ally in the region to advance shared prosperity, values and security, before ending with a phrase symbolizing the alliance, "Katchi Kapshida," meaning "We go together."