The Cheonan sank after an as-yet unexplained blast on 26 March
South Korea's defence minister has confirmed that traces of an explosive have been found in the wreckage of a warship that sank near North Korea.
Kim Tae-young said that RDX - used to make torpedoes - was detected by investigators.
But he said it was too early to draw conclusions about what sank the ship.
The Cheonan went down on 26 March near the disputed inter-Korean maritime border. Many South Koreans believe North Korea was to blame.
"It is true that RDX, a chemical substance used in making torpedoes, has been detected," Mr Kim told reporters.
"The possibility of a torpedo (attack) has increased, but it's too early to say anything."
A spokesman for the investigative team, Rear Adm Moon Byung-ok, said mines used RDX too, so further examination was necessary.
He said the explosive traces were found in the Cheonan's funnel and in sand collected from the seabed.
The defence minister called on South Koreans to "be patient and wait until the official announcement is made".
Forty-six South Korean sailors were killed when the Cheonan sank. North Korea has denied any responsibility for the incident.
The two countries' navies have clashed around the disputed maritime border in the past. They remain technically at war, because no peace deal was signed after the 1950-53 Korean War.