South Korea's President Lee Myung-Bak urged China Wednesday to follow international norms in handling North Korean refugees, as his government pressed Beijing not to repatriate them.

Lee also accused the North of trying to incite divisions within his country to sway elections later this year but said the tactic would not work.

His first comments on the refugee issue came a day after the South said it would seek UN support to try to prevent refugees recently detained in China from being sent back.

Human rights activists in Seoul say returnees face severe punishment or even the death sentence. They say China's policy breaches international refugee conventions, an assertion denied by Beijing.

"The relevant people entered China illegally due to economic reasons. They are illegal border crossers, they are not within the category of refugees," China's foreign ministry spokesman Hong Lei said Tuesday.

China opposes "the internationalisation and the politicisation of this issue", the spokesman added Wednesday.

The activists, along with lawmakers and teenage former defectors, have held a series of rallies outside China's embassy in recent days. They say some 30 refugees detained recently face imminent repatriation.

"When it comes to the North Korean defectors, it is right for the Chinese government to handle them in line with international rules as long as they are not criminals," Lee told a press conference.

The South Korea and Chinese foreign ministers plan to meet in Seoul soon, Seoul's foreign ministry said. The refugee issue was expected to figure high on the agenda.

Lee's press conference was to mark the fourth anniversary this week of his inauguration.

Inter-Korean relations have been icy since the conservative former business executive scrapped the "sunshine" aid and engagement policy towards the North of the previous centre-left government.

Lee has said there is a "window of opportunity" for better ties after the death of the North's longtime leader Kim Jong-Il in December, and the takeover by his son Jong-Un.

The new regime has however rejected several offers of dialogue from Seoul.

The South is ready to talk to its neighbour with an "open heart" if Pyongyang is also willing to talk sincerely, Lee said Wednesday.

But he said the North is trying to sway the outcome of a general election in the South in April, followed by a presidential poll in December.

"The North is trying to influence the election by sparking various feuds within the country (South Korea)," Lee said. "The South's voters are not swayed by such things."

This week the North's military threatened a possible attack in retaliation for a South Korean artillery exercise near the disputed Yellow Sea border. Monday's drill passed without incident.

On Wednesday the North blasted the upcoming nuclear security summit in Seoul as a "childish farce" and a grave provocation.

A statement on the official news agency said the meeting would be "one more childish farce whereby the US and the (Seoul) puppet group seek to escalate the anti-DPRK (North Korea) nuclear racket".

It said the March 26-27 event was intended to "justify the nuclear war moves" against the North and help the conservatives win the elections.

South Korea says the summit, to be attended by US President Barack Obama and about 40 other world leaders, is unlikely formally to discuss the North's nuclear programme.

It says the agenda will focus on ways to safeguard atomic material worldwide and to prevent acts of nuclear terrorism.

US and South Korean officials will Thursday hold talks in Beijing aimed at reviving six-nation negotiations on the North's nuclear disarmament.

The North has frequently said it needs atomic weaponry to counter a nuclear threat from the United States.