South Korea blamed North Korea for sinking a naval ship ahead of an official report on the fatal incident to be released this week.

"In a search using fishing trawlers we recently discovered pieces of debris that are believed to have come from the propeller of the torpedo that attacked the Cheonan," an unnamed high-ranking government source told South Korean journalists.

"U.S., Australian and other foreign experts who took part in the investigation agree that a North Korean torpedo caused the Cheonan to sink and that this is the smoking gun following various pieces of the torpedo and traces of gun powder that had been gathered so far," the official said.

South Korea's Foreign Minister Yu Myung-hwan also said there was enough evidence to make it "obvious" that North Korea was involved.

Forty-six sailors died when the Cheonan rapidly sank in shallow waters March 26 after an explosion ripped the vessel in half.

The 1,200-ton naval corvette sank just more than 1 mile southwest of Baeknyeong Island near the de facto sea border with North Korea.

North Korea consistently denies it had anything to do with the sinking.

But the incident has increased tensions between the two countries divided in an uneasy cease-fire since the end of a three-year war in 1953 between the communists in the north and the southern forces.

The current remarks blaming North Korea outright come after comments earlier this month by South Korea's Defense Minister Kim Tae-young who tried to dampen rising speculation over the sinking.

After traces of the powerful explosive RDX were found in parts of the raised hulk of the Cheonan, Kim urged media to wait for the publication of the independent investigating team.

"Controversy sparked by groundless speculations could have a negative influence on our moves to deal with the incident after the investigation result comes out," Kim said at the time. "This is a matter that should be approached based on objective facts."

He said there is no concrete evidence that the ship was the victim of a torpedo attack, as has been speculated.

"It is still premature to make any conclusion although the possibility of a torpedo is high. Please wait until the investigation team gives a detailed explanation," Kim said.

South Korean government officials reportedly met this week to discuss specific sanctions against North Korea including joint anti-submarine exercises by South Korean and U.S. forces and a trade embargo.

But trade with the Kaesong Industrial Region, a joint north and south project set up in 2002, would remain intact. The special economic region is within North Korea and about 6 miles from the demilitarized zone separating two states. It has direct rail access to the south and is about an hour's drive from the South Korean capital Seoul.

Both Koreas benefit from the trade with the cash-strapped North gaining more than $33 million year. About 100 South Korean companies are based in the Kaesong region and employ 40,000 North Koreans.

The North also announced this week that its Supreme People's Assembly, the nation's rubber stamp Parliament, is to meet for an extraordinary session on June 7.

No reason was given for the meeting of the assembly, which usually gathers only once a year. Analysts said it might be to prepare responses to any moves by the south to isolate it over the Cheonan incident.

Analysts also speculated that the meeting might be to hand over more responsibilities to Kim Jong Un, the favored son of the aging and presumed ailing North Korean leader Kim Jong Il.

earlier related report
S.Korea minister blames N.Korea for warship sinking
Seoul (AFP) May 19, 2010 - Seoul's foreign minister said Wednesday it was "obvious" North Korea had fired a torpedo which sank a South Korean warship, leaving 46 sailors dead in one of the country's worst naval tragedies.

The comments by Yu Myung-Hwan came a day before a multinational investigation team announces its findings on the March 26 explosion, which blew a 1,200-tonne corvette in two near the disputed sea border.

Top South Korean officials had previously hinted strongly that the North was involved. Yu was the first publicly to implicate the hardline communist state, which denies involvement.

Asked by reporters whether the North had sunk the Cheonan, Yu replied: "I think it's obvious." Seoul has "enough evidence" to bring the issue to the United Nations Security Council, he added.

The North's official Korean Central News Agency quoted Pyongyang's Committee for the Peaceful Reunification of Korea, as saying the "South Korean puppet group" was using the sinking as a "golden opportunity for pushing the north-south relations to a catastrophe".

"Making the fiction that the accident 'was caused by the north' a fait accompli from its beginning, the group cried out for 'countermeasure' and 'retaliation,'" it claimed.

"Should the group of traitors ignite a war together with the US at any cost, the DPRK will mete out merciless and resolute punishment to the warmongers," KCNA quoted the committee as saying in a statement.

South Korea has been seeking firm proof its neighbour sank the warship, in what would be the bloodiest provocation since the North's agents downed a South Korean airliner in 1987 with the loss of 115 lives.

President Lee Myung-Bak told Japanese Prime Minister Yukio Hatoyama Seoul has indisputable evidence of who was responsible.

Lee, according to his spokesman, told Hatoyama in a phone conversation "clear and definitive material evidence will be presented that no country in the world and no one can refute".

Media reports say explosive traces found on the Cheonan and on the seabed have a similar chemical make-up to substances found in a stray North Korean torpedo secured by the South seven years ago.

Yu said in a speech earlier Wednesday that investigators, including experts from Britain, Sweden, the United States and Australia have confirmed the corvette was hit by a torpedo.

Seoul would take "firm and prudent" measures to deter "any future provocations which will undermine peace and stability in Northeast Asia", he told the European Union Chamber of Commerce, appealing for international support.

In search of that backing the foreign ministry Wednesday briefed diplomats from some 30 countries about the findings of the investigation. Envoys from China, Japan and Russia had been briefed a day earlier.

South Korea is likely to ask the Security Council to slap new sanctions on the North, in addition to those imposed to curb its missile and nuclear programmes.

But China, a veto-wielding council member and the North's ally, is unlikely to support new measures unless the South produces a "smoking gun" linking its neighbour to the attack.

North and South Korea have remained technically at war since their 1950-53 conflict ended only in an armistice. The land border is closely guarded.

The North refuses to accept the borderline drawn in the Yellow Sea, where the Cheonan went down. The area was the scene of deadly clashes in 1999 and 2002 and of a firefight last November which left a North Korean patrol boat in flames.

Some analysts suggest the attack on the Cheonan was revenge for the November clash.

Vice Unification Minister Um Jong-Sik said the sinking "shows the cruel reality of the division and the reality of security on the Korean peninsula.

"Improvement in inter-Korean relations cannot be expected while national security is threatened," he said.

The United States, which has 28,500 troops in the South, has given its ally strong backing.

US President Barack Obama and South Korea's President Lee Myung-Bak, in a telephone conversation Monday, said the North should end "belligerent behaviour towards its neighbours".

They stopped short of blaming it for the sinking but said they are committed "to follow the facts of the investigation wherever they lead".