South Korean President Moon Jae-in and North Korean leader Kim Jong-un have been exploring ways to improve strained ties by exchanging multiple letters since April, the sources said on condition of anonymity due to diplomatic sensitivity.

The discussions signal an improvement in ties that have deteriorated in the past year after three leaders' summits in 2018 promised peace and reconciliation.

Inter-Korean talks could also help restart stalled negotiations between Pyongyang and Washington aimed at dismantling the North's nuclear and missile programs in return for sanctions relief.

The issue is key for Moon, who is facing declining support in his final year in office. Moon staked his legacy on improving relations with North Korea and helped set up historic meetings between Kim and then US President Donald Trump in 2018 and 2019.

The two Koreas, still technically at war after their 1950-53 conflict ended in a ceasefire, on Tuesday reconnected hotlines the North severed in June last year.

Both sides are discussing rebuilding their joint liaison office at the truce village of Panmunjom on the border, two sources said. Pyongyang spectacularly destroyed the previous office in its border town of Kaesong in 2020.

They are also seeking a summit between Moon and Kim, but no time frame or other details have been raised due to the coronavirus pandemic, the sources said.

North Korea has not confirmed any COVID-19 cases, but it shut borders and imposed strict prevention measures, seeing the pandemic as a matter of national survival.

"The talks are still ongoing, and COVID-19 should be the biggest factor," one source said. "A face-to-face meeting is the best, but hopefully the situation will get better."

Moon's office referred to a briefing on Tuesday by his press secretary, Park Soo-hyun, who said the issue of restoring the liaison office was to be discussed, and that the leaders have not floated plans for any summit so far.

A second source said a virtual summit could be an option depending on whether North Korea balks at a meeting in person because of COVID-19.

"If we can do that and the North has that capability, it would make a big difference, and open so many windows of opportunity, something to restart talks with the United States."

Moon had called for a revival of the hotlines and offered a video summit with Kim, but Pyongyang had previously responded publicly with scathing criticism, saying it had no intention of talking to Seoul.

The first source said Moon and Kim have exchanged "candid" letters on more than 10 occasions, which led to an opening of a communication channel between Seoul's intelligence authorities and Kim's sister, Kim Yo Jong.

Despite "ups and downs" in the consultations, the two sides agreed over the weekend to reactivate hotlines as a first step.

Kim's move reflected a willingness to respond to US overtures for talks, as the administration of President Joe Biden vowed a practical approach including not naming an envoy for North Korean human rights issues, the source said.

Washington supports inter-Korean engagement, and diplomacy is essential to achieving complete denuclearisation and lasting peace on the Korean peninsula, a spokesperson said on Tuesday in welcoming the opening of the hotlines.

Australian Associated Press