South Korea has said it conveyed a message from US President Donald Trump to North Korean leader Kim Jong Un wishing him a happy birthday, which is believed to be on January 8.

Returning from a visit to Washington, South Korea’s presidential national security director Chung Eui-yong said Trump requested that Seoul deliver the message to Kim during a meeting at the White House this week.

Chung did not disclose what the message specifically said, but said Seoul sent it to Pyongyang on Thursday through “proper means”.

Kim last week opened the new year expressing deep frustration over stalled nuclear negotiations with the Trump administration and vowed to bolster his nuclear arsenal as a deterrent against “gangster-like” US sanctions and pressure.

The North in past months has severed virtually all co-operation with the South, while demanding Seoul break away from Washington and restart inter-Korean economic projects held back by US-led sanctions.

But the Koreas still operate a liaison office in the North Korean border town of Kaesong.

Seoul had lobbied hard for the resumption of nuclear negotiations, with Chung shuttling between Pyongyang and Washington to help set up the first summit between Kim and Trump in June 2018. But negotiations have faltered since the collapse of the second Kim-Trump meeting in February last year, when the US side rejected North Korean demands for major sanctions relief in exchange for a partial surrender of its nuclear capabilities. Despite the standstill in talks, Trump and Kim have both described their personal relationship as good.

Trump has boasted about the “beautiful” letters he has received from Kim.

North Korea has never officially confirmed Kim’s birth date.

While covering a 2014 visit to the country by basketball player Dennis Rodman, North Korean state media said the former NBA star organised an exhibition game on January 8 to celebrate Kim’s birthday.