SEOUL (REUTERS) - North Korea rejected an invitation for leader Kim Jong Un to attend a planned summit in Seoul with South-east Asian nations next week, saying "now is not the time" due to strained ties, North Korean state media reported on Thursday (Nov 21).

South Korean President Moon Jae-in sent a letter of invitation to Mr Kim on Nov 5, with an offer for an envoy to attend if he was unable to participate in the event, the official KCNA news agency said.

Mr Moon will host leaders of Asean in the South Korean port city of Busan next week to celebrate the 30th anniversary of their partnership, and has said Mr Kim might join them.

While thanking Seoul for the invitation, North Korea requested the South's "understanding that we could not find any legitimate reason" for Mr Kim to participate, KCNA said.

The statement accused South Korea of harming relations by depending on the United States in resolving inter-Korea issues.

"It is perplexing that they proposed discussing inter-Korean relations at such an unfitting multilateral venue, even after experiencing failures by relying so much on the United States," KCNA said.

The two Koreas undertook a flurry of diplomacy, including three summits, last year, during which Mr Moon and Mr Kim agreed to improve ties and restart stalled business initiatives.

But there has been no significant progress amid tightening sanctions aimed at the North's nuclear and missile programmes, and lacklustre denuclearisation talks between Pyongyang and Washington.