US Secretary of State Mike Pompeo has sent a letter thanking South Korea for helping his country purchase Korean-made coronavirus test kits, saying such a partnership is a testament to the "strong and unshakable" alliance, Seoul officials said.

The letter, addressed to Foreign Minister Kang Kyung-wha, came after the US Federal Emergency Management Agency (FEMA) purchased the test kits, enough to run 750,000 tests, from three South Korean companies early this month.

The shipments followed the preliminary approval of the diagnostic tools for emergency use by the US Food and Drug Administration (FDA), amid a rapid spread of the COVID-19 outbreak across the United States.

"I thank the ROK for its assistance to the American people in facilitating the purchase of 750,000 COVID-19 tests," he said in the letter, referring to South Korea by its official name, the Republic of Korea. "I am grateful for the rapid response of your government and the three private Korean companies that made this vital procurement possible."

The letter was delivered to Kang late last week, officials said.

Pompeo then went on to highlight the value of alliance at a time of crisis, saying that such close coordination is "fundamental to executing a swift and effective response."

"The partnership between our nations to address this crisis reflects the strong and unshakable bonds of our alliance," he added.

He also lauded South Korea's anti-virus responses as a global model.

"Your country has been an exemplary global model by rapidly establishing comprehensive measures to contain the spread and transmission of the virus."

Pompeo has left a similar message of gratitude in a reply to a recent tweet by US Ambassador Harry Harris, in which the top US envoy welcomed Hyundai Motor Co.'s $4.3 million donation to the US to help develop drive-thru testing at 22 hospitals. (Yonhap)