Seoul is "paying attention to Carter's plan to visit North Korea," foreign ministry spokesman Cho Byung-Jae told reporters, calling it "a personal trip."

"All the communications currently under way for the visit are purely private talks... and the US government also said his trip would be a personal visit," he said.

Carter has been in talks with the North's UN mission in New York to arrange his trip to Pyongyang, Yonhap news agency said.

"He will likely visit the North about a month later," a diplomatic source was quoted as saying.

Former UN Secretary General Kofi Annan, ex-Irish president Mary Robinson and former Norwegian prime minister Gro Harlem Brundtland may go together with Carter, Yonhap said.

The 2002 Nobel Peace Prize laureate made a landmark visit to Pyongyang in 1994 when the US came close to war with North Korea over its nuclear programme, helping defuse the crisis through talks with then-leader Kim Il-Sung.

He also visited the isolated communist state in August last year to secure the release of an American held there for illegal entry.

Tension is high on the peninsula marking the first anniversary of the North's alleged sinking of a South Korean warship that killed 46 sailors.

South Korea launched a major live-fire drill Thursday near the tense land border with the North. It is also holding a week-long sea exercise that began on Monday to mark the anniversary.

Security fears increased further after Pyongyang last November shelled a border island and disclosed an apparently functional uranium enrichment plant to visiting US experts.

Pyongyang said the plant was a peaceful energy project, but experts warned it could be reconfigured to make weapons-grade uranium, giving the North a second way to produce bombs on top of its plutonium-based weapons.