Kim Jong Un offered condolences for the death of a former first lady of South Korea. (File)

North Korean leader Kim Jong Un sent his sister to the border with South Korea on Wednesday to offer condolences for the death of a former first lady, in the first significant interaction between the two countries in months.

Kim Jong Un's younger sister, Kim Yo Jong, who holds a senior position in the government, brought a wreath and a letter of condolence from her brother after the death of former South Korean first lady Lee Hee-ho on Monday.

She was seen smiling broadly and shaking hands with South Korean officials before sitting across a table and handing over a purple folder containing the condolence letter. Their 15-minute meeting was the first high-level interaction between the two Koreas since the breakdown of a summit in Hanoi between Kim Jong Un and President Donald Trump at the end of February.

South Korea's national security adviser, Chung Eui-yong, quoted Kim Yo Jong as saying that she hoped for a continuation of the inter-Korean cooperation that the late first lady had worked for.

In the letter, which was later read at Lee's funeral, Kim Jong Un praised her devotion and efforts, along with her husband, the late president Kim Dae-jung, "for the reconciliation and unity of the people, and peace and unification of the nation, in face of all the hardships and troubles."

Those efforts, he said, "serve as a precious foundation to current flow of the inter-Korean relationship that is proceeding toward autonomous reunification and prosperity, and the people will never forget about it."

The meeting followed another letter sent by Kim to Trump on Monday, marking a slight thaw in North Korea's position since the Hanoi summit. In the interim, North Korea has tested short-range ballistic missiles, rebuffed several attempts by Washington and Seoul to resume talks and issued a serious of angry statements on state media.

On Tuesday, Trump described Kim's missive as a "beautiful letter," adding that it was "very personal, very warm, very nice."

Wednesday marked exactly a year since Trump first met Kim in Singapore. It had looked to be a gloomy anniversary given the breakdown in dialogue, but this week's developments offered a glimmer of hope.

Speaking on a trip to Norway, South Korean President Moon Jae-in urged Trump and Kim Jong Un to meet for a third summit as soon as possible. Trump is due to travel to Seoul later this month, after attending a Group of 20 summit in Japan on June 28-29.

South Korea's Yonhap state news agency said an inter-Korean summit before Trump's visit could present a "golden opportunity" to move the talks forward.

Moon said such a meeting would be "desirable" but added that it was up to Kim Jong Un to decide.

South Korean presidential adviser Moon Chung-in told a news conference on Wednesday that Kim's letter opened a "new possibility" between Washington and Pyongyang.

But several experts were more skeptical, welcoming the shift from military posturing to dialogue but arguing that there was no sign of change in North Korea's negotiating position.

They said a third Trump-Kim summit without meaningful working-level talks beforehand would raise the risks of another embarrassing failure.

Soo Kim, a policy analyst at the Rand Corp. and former CIA analyst, said North Korea was following a "well-rehearsed playbook," involving dramatic, inflammatory rhetoric, placing the blame on Washington for the breakdown in talks, missile launches, playing hard to get, and arm-twisting Seoul.

"Once you have Washington's attention, simmer down a bit and do something nice enough to once again condition your counterpart to talks - or rather, weaken their resolve and muddy their judgment to be able to discern sincerity," she said.

"Patently, the letter should not be mistaken for North Korea coming around to a more reasonable position to negotiate. A third summit is unfortunately not going to be the charm for us."