North and South Korea have presented their cases to the UN in a dispute over the sinking of a Southern warship.
Seoul asked the UN to take "timely and appropriate measures", blaming Pyongyang for March's sinking of the Cheonan, which killed 46 sailors.
But the North denied involvement and said it was the victim.
After hearing separate submissions from both sides, UN officials said they had "grave concern" over the issue and needed to debate it further.
"The Security Council makes a strong call to the parties to refrain from any act that could escalate tensions in the region," said the council in a statement.
The South Koreans presented evidence, including a Powerpoint presentation, which they said showed their warship was sunk by a North Korean torpedo.
"We hope that on the basis of this finding the Security Council will take timely and appropriate measures against North Korea," said South Korean delegate Yoon Duk-yong.
UN diplomats said the North Koreans demanded an opportunity to visit the site of the explosion, and once again rejected South Korea's allegations as forgery and fraud.
"We are just a victim, we would like to make our position clear here, we will inform our position, concerning that issue," said Pak Tok-hun, the North's deputy UN ambassador.
Yukio Takasu, Japan's ambassador to the UN, said South Korea's argument that North Korean was behind the sinking was "extremely convincing". He added that there was "very little substance" to back up North Korea's claim that it was the victim in the incident.
Officials in Seoul will be pleased with that response, says the BBC's John Sudworth in the South Korean capital.
They will be hoping that their case was so strong that it leaves no doubt in the minds of Security Council members as to North Korea's culpability, our correspondent says.
South Korea hopes the next step will be a strong statement from the council outlining some form of action against North Korea, he adds.
But there is still no agreement on what to do, as Security Council members China - North Korea's strongest ally - and Russia have not yet commented on the investigation.
The warship row has left inter-Korean relations highly tense. Seoul has suspended inter-Korean trade and Pyongyang responded by cutting all ties.