* South, North brief Security Council separately
* Seoul wants "timely and appropriate measures" from UN
* North Korean ambassador to hold news conference Tuesday (Adds South Korean official, Japan envoy; paragraphs 10, 13)
By Louis Charbonneau
UNITED NATIONS, June 14 (Reuters) - The U.N. Security Council expressed grave concern on Monday over the deadly sinking of a South Korean naval ship in March that has heightened tension on the Korean peninsula.
Seoul, which has accused North Korea of torpedoing the corvette Cheonan on March 26, killing 46 sailors, brought the dispute to the Security Council this month, asking the 15-nation body to take action to deter "further provocation."
Mexican Ambassador Claude Heller, president of the council this month, read out an agreed statement to reporters after two separate informal briefings from South and North Korean delegations on the incident.
"The Security Council is gravely concerned with this incident that caused the death of 46 sailors and its impact on peace and stability on the Korean peninsula," Heller said. The careful wording did not say who was to blame for the incident.
"The Security Council makes a strong call to the parties to refrain from any act that could escalate tensions in the region and makes an appeal to preserve peace and stability in the Korean peninsula," he said. "The Security Council will continue its consultations on this incident."
Council diplomats say that South Korea is hoping the council will rebuke the North, though North Korea’s sole major ally, China, wields veto power on the council and is reluctant to support any action or statement that would upset Pyongyang.
North Korea, which denies responsibility and accuses the South of fabricating the attack, asked Heller for a separate briefing session after the South Koreans asked to present the results of an international investigation to the council.
South Korea went in first. Civilian and military officials made a detailed technical Powerpoint presentation to the closed-door meeting followed by a question-and-answer session, diplomats who attended the two-hour meeting said.
"We presented and explained to the U.N. Security Council the evidence that the Cheonan was sunk by a torpedo which was made in North Korea and the launching was also done by a midget North Korean submarine," the co-head of the investigation, South Korean physics professor Yoon Duk-yong, told reporters.
He said he hoped the council would "take timely and appropriate measures against the provocation of North Korea."
A senior North Korean envoy rejected the South’s case.
"We have nothing to do with that. We have nothing to do at all. We are just a victim. So we would like to make our position clear here," Deputy Ambassador Pak Tok-hun told reporters. He said Ambassador Sin Son-ho would give further details at a rare news conference at the United Nations on Tuesday.
Japanese Ambassador Yukio Takasu said there was "very little substance" in what the North Koreans told the council.
Mounting antagonism between the Koreas has worried investors, concerned about armed conflict breaking out, and set off a diplomatic scramble on all sides to cool tension.
Many analysts say neither side is ready to fight, despite frequent threats of all-out war from the North, but see the possibility of more skirmishes in a disputed sea border area off the west coast or along their heavily armed land border.
South Korea accused the North of violating the spirit of a landmark joint declaration struck by then-South Korean President Kim Dae-jung and North Korean leader Kim Jong-il 10 years ago pledging peace. That summit in Pyongyang led to warming ties and the beginning of trade between the rivals.
South Korean President Lee Myung-bak cut aid to the North when he took office in 2008, demanding Pyongyang drop its nuclear ambitions. That move angered its destitute neighbor.
The South’s Unification Ministry spokesman, Chun Hae-sung, said the North must admit its role in the naval attack and apologize if it wants to see the ties reinstated. Pyongyang says the accusations are part of a U.S.-led plot.
A team of international investigators, led by South Korea’s military, said in May that a North Korean submarine torpedoed the ship.
In the first in what some believe will be a string of high ranking military officers to be replaced over the ship sinking, South Korea’s chairman of the Joint Chiefs of Staff was replaced on Monday for a perceived slow response.
South Korea’s liberal opposition has been calling for the dismissal of the defense minister and other senior military officials, but so far Lee has resisted.
North Korea repeated its threat to blow up loudspeakers South Korea has set up at the border to broadcast anti-Pyongyang propaganda, keeping tension on the peninsula at its highest in years. (Additional reporting by Patrick Worsnip at the United Nations and Jack Kim in Seoul; editing by Mohammad Zargham and Chris Wilson)