The South Korean naval ship Cheonan

United Nations Security Council President Claude Heller said that the U.N. body is "gravely concerned" about tensions between North Korea and South Korea after hearing
presentations from both sides Monday into the sinking of a South Korean naval ship in contested waters in March.

After their presentation, civilian and military members of the South Korean investigative panel called on the council to "take timely and appropriate measures" against Pyongyang for its role in the alleged attack.

Heller said the council is concerned over the potential "impact on peace and stability on the Korean peninsula" as a result of the March 26 sinking of the Cheonan ship. Forty-six sailors died in the incident.

"We presented and explained to (the council) the evidence that the Cheonan was sunk by a torpedo, which was made in North Korea, and launching was also done by a North Korean ... submarine," said Yoon Duk-yong, a science and physics professor serving as a civilian expert on the South Korean panel.

Yoon said the findings were based on evidence recovered after the sinking, including an intact piece of the torpedo with propellers, steering plates and a motor.

"We hope that on the basis of these findings," he said, "the Security Council will take timely and appropriate measures against the provocation of North Korea against the naval ship of the Republic of Korea."

The council is calling on both sides "to refrain from any act that could escalate tensions in the region," Heller said.

The two-hour meeting was held behind closed doors Monday afternoon and was also attended by U.S., Australian, British, Swedish and Canadian scientific experts who had participated in the investigation.

The Japanese ambassador to the U.N. made brief remarks following the two nations' presentations, saying "there is no other explanation" than that the South Korean ship was sunk by a North Korean torpedo.

"I think the council should react in a decisive manner, but at the same time try to avoid any act which may provoke" a retaliatory attack, Ambassador Yukio Takasu said.

North Korea has repeatedly denied any responsibility in the sinking, and Takasu said Monday that the North's defense of the incident contained "very little substance."

"Basically they claimed that it is not South Korea, but North Korea that is the victim," Takasu said, adding that when pressed, the North's delegation couldn't elaborate further on the allegation.

Heller said a decision has not yet been made on how to respond to the incident.

"The Security Council will continue its consultations," he said.