WASHINGTON, April 20 (Reuters) - The United States will continue to coordinate closely with South Korea on more support for Ukraine, calling its key Asian ally "a stalwart partner" in defending Ukraine's sovereignty, a U.S. State Department spokesperson said.

In an exclusive interview with Reuters, South Korean President Yoon Suk Yeol said the country might go beyond humanitarian or financial aid for Ukraine under certain circumstances, signalling a shift in his stance against arming Ukraine for the first time.

"The ROK (Republic of Korea) has been a stalwart partner in defending Ukraine's right to territorial sovereignty against Russian aggression from the earliest days of the full-scale invasion," a U.S. State Department spokesperson said in an emailed response to Reuters, when asked about Yoon's comments.

The spokesperson didn't want to be identified by name.

The Republic of Korea is South Korea's official name.

"We will continue to coordinate closely with our ally on additional support for Ukraine," the spokesperson said.

A key U.S. ally and major producer of artillery ammunition, South Korea has so far tried to avoid antagonising Russia due to its companies operating there and Moscow's influence over North Korea, despite mounting pressure from western countries for weapons supply.