South Korea reacted coolly Monday to North Korea's latest offer of dialogue, telling the communist country to show sincerity and act to ease high tensions.

The North -- in its latest apparent peace overture less than two months after a deadly bombardment of a South Korean island -- on Saturday proposed an "unconditional and early opening" of talks.

Tensions soared after the North shelled the border island on November 23 and killed four people including civilians.

Seoul's unification ministry, which handles cross-border relations, played down the latest message.

"It's hard to consider it as a sincere offer of dialogue," said spokesman Chun Hae-Sung, adding the North should first show it is serious about nuclear disarmament.

"North Korea must also take responsible steps our people can accept" over the shelling and the sinking of a South Korean warship in March last year, Chun said.

The South says the North torpedoed the ship near the disputed Yellow Sea border with the loss of 46 lives, a charge it denies.

In a New Year message, Pyongyang had called for improved relations with Seoul. Last week the South's President Lee Myung-Bak said he was open to talks and held out the prospect of closer economic ties "if the North exhibits sincerity".

Pyongyang's Committee for the Peaceful Reunification of the Fatherland said Saturday there was "neither conditionality in the North's proposal for dialogue nor need to cast any doubt about its real intention".

The committee's proposal was seen as more formal than earlier overtures, but South Korea wants a request through official channels.

"The door for dialogue is open if North Korea shows a sincere attitude," Chun said, adding that Seoul would review the North's proposal after monitoring its behaviour.

Analysts said the overtures follow US demands that the North improve relations with the South before six-party nuclear disarmament talks resume.

The North quit the forum in April 2009 and staged a nuclear test a month later, its second since 2006.

It has expressed conditional willingness to return to dialogue, but raised security fears last November by disclosing a uranium enrichment plant to visiting US experts.

The North says the plant is designed to fuel peaceful power generation but experts say it could easily be reconfigured to make weapons-grade uranium.

"North Korea must take actions instead of words about denuclearisation," Chun said.

The Korea JoongAng Daily said Monday that Seoul would first test Pyongyang's sincerity by seeking United Nations Security Council action over the uranium programme.

"It is based on the judgment that we could move forward toward dialogue with North Korea only after easing some of the anti-North Korean sentiment at home as a result of the Security Council action," an unnamed foreign ministry official was quoted as saying.

The official said that if the North strongly resists a Security Council measure, it will prove that its offer of dialogue is "only a tactic to divert attention".

A foreign ministry spokesman refused to confirm the report but said Seoul "hopes the international community will take a stern response to North Korea's uranium enrichment".

Defence Minister Kim Kwan-Jin and his Japanese counterpart Toshimi Kitazawa held talks Monday on security issues such as the North's nuclear programme and ways to enhance military cooperation.

earlier related report
S. Korea, Japan explore deeper defence ties
Seoul (AFP) Jan 10, 2011 - The South Korean and Japanese defence chiefs held talks Monday on strengthening military ties, despite historical animosities, in the face of a nuclear-armed North Korea.

Military officials said the meeting focused on regional security issues such as the North's nuclear programme and ways to enhance military cooperation between Seoul and its former colonial ruler.

The meeting between Defence Minister Kim Kwan-Jin and his Japanese counterpart Toshimi Kitazawa comes amid high regional tensions over the North's deadly shelling of a South Korean island in November.

Earlier that month, the North disclosed the existence of a uranium enrichment plant which could be converted to military use.

The United States has staged military drills with both South Korea and Japan, in a show of strength around the peninsula.

The South's defence ministry said the two sides, at working-level talks before the ministerial meeting, discussed signing two agreements to share military secrets and exchange military goods and services for peacekeeping, relief operations and exercises.

The two countries have signed separate agreements with the United States to share classified military information, but have no such deal between themselves.

In 2009 Seoul and Tokyo signed a memorandum of understanding on comprehensive military cooperation.

But South Korea has long been reluctant to work too closely with Japan's military amid lingering bitter memories of the 1910-45 annexation.

Apart from history, ties have been strained by Tokyo's reasserted claims over a chain of Seoul-controlled islands in the Sea of Japan (East Sea).

On Tuesday Kitazawa will visit the border truce village of Panmunjom and a naval base in Pyeongtaek, 70 kilometres (45 miles) south of Seoul, to see the wreck of a warship allegedly sunk by a North Korean torpedo attack in March.

Japan's centre-left Prime Minister Naoto Kan and South Korean President Lee Myung-Bak may sign a joint statement centred on security cooperation as early as this spring, the Yomiuri Shimbun daily reported earlier.