South Korea and the United States have been working together to fill the post of US ambassador to Seoul as soon as possible, the foreign ministry said.

"With the understanding that an early arrival of a US ambassador to South Korea is desirable, the governments of South Korea and the US have been cooperating to that end," the ministry's deputy spokesperson Kim Deuk-hwan said.

The Washington Post reported a day earlier that Adm. Harry Harris, the commander of the US Pacific Command, who was previously nominated as the US ambassador to Australia, has been newly chosen as the ambassador to South Korea. Australian Foreign Minister Julie Bishop was also reported to have been informed of the decision from the US side.

"As far as I know, the US side has not officially made the nomination yet," Kim said, adding that the allies are continuing to cooperate on the issue.

The US ambassador's seat has been left empty for more than a year since the last envoy, Mark Lippert, vacated the seat with the inauguration of President Donald Trump in January last year.

The urgency to fill the void has increased as Trump is poised to hold the first-ever US-North Korea summit with Kim Jong-un in May or early June for a possible breakthrough in the North's long-running nuclear issue.(Yonhap)