North Korea warned the UN Wednesday of "serious" consequences for peace if it debates an alleged torpedo attack on a South Korean warship without letting the North's investigators examine the evidence.

South Korea, the United States and other countries accuse the North of sinking the ship with the loss of 46 lives and are pushing for the United Nations Security Council to censure the communist state.

The North accuses Washington and Seoul of a "smear campaign" to fake evidence of its involvement as a pretext for aggression and says reprisals already announced by the South could spark war.

Pyongyang said Wednesday its UN representative had written to the council president, repeating demands that it be allowed to send a team south of the border to examine the evidence.

"In case the unilaterally forged 'investigation result' is put on the agenda of the United Nations Security Council and open to be debated without the verification of the directly victimised party...no one would dare imagine how serious its consequences would be with regard to the peace and security on the Korean peninsula," state media quoted the letter as saying.

It urged the Security Council not to be swayed by US "lies" as it was over the invasion of Iraq in 2003 and said the world body has a duty to stay impartial.

After a weeks-long investigation a multinational team said last month there was overwhelming evidence that a North Korean submarine had fired a heavy torpedo to break the warship in two in March.

South Korea formally asked the Security Council last week to respond and said Wednesday the investigators would brief the council's 15 members on the probe at the request of council president Mexico.

The South has rejected the North's demands to send its own investigators, with the defence minister saying it would be "like a robber or a murderer insisting he must inspect the crime scene".

The South has announced reprisals, including cutting off trade with the cash-strapped North, and is lobbying for support at the UN.

It can expect backing from the US, Britain and France but China and Russia, the other two veto-wielding permanent council members, have not publicly stated their positions.

Seoul's Vice Foreign Minister Chun Yung-Woo returned Wednesday from a trip to lobby China, which so far has not publicly condemned its ally the North.

"We had preliminary discussions on core issues regarding the nature and the content of measures we would like to pursue at the Security Council," he told reporters without elaborating.

Chun said the two countries still had differences. "We agreed to keep working toward reaching acceptable solutions, based on our strategic cooperative partnership."

South Korea has announced plans to resume cross-border loudspeaker propaganda broadcasts as part of its reprisals. The North says it will fire at the speakers if it does so.

The South Wednesday completed installing the loudspeakers along the tense border but has not decided when to switch them on, Yonhap news agency quoted an unidentified military official as saying.

The South's government gave the go-ahead for two aid shipments of baby formula to the North despite the rising tensions.

The unification ministry said the shipments from private groups of milk and other items totalling 320,000 dollars would be sent late this month.

The impoverished North suffers severe food shortages. The UN Children's Fund says one in three of its children is stunted by malnutrition.