Privately, U.S. officials acknowledged the findings will have major ramifications for U.S. policy in Asia. They worry that further escalations by the North could complicate an American foreign policy agenda dominated by the war in Afghanistan and international efforts to contain Iran’s nuclear program.
North Korea has been angry with South Korea since the 2007 election of Mr. Lee, who ended 10 years of providing money to the North.
More broadly, North Korea has pushed forward the development of nuclear weapons and advanced missiles against the wishes of the South and the Obama administration.
It has chafed under stricter penalties imposed by the U.N. Security Council after a nuclear test last May, which have resulted in the seizure of weapons shipments that are a main source of cash for dictator Kim Jong Il’s regime.
Many in South Korea speculate that the March 26 sinking may have been retaliation for a fire fight last November when South Korea’s navy severely damaged a North Korean vessel and perhaps killed some of its sailors.
That skirmish occurred in the boundary area not far from where the Cheonan sunk. The North’s dictator Mr. Kim visited the navy base of the damaged ship in February.
In another line of speculation, some analysts say Mr. Kim may have ordered the attack to show strength inside the country to help the potential succession of his son, Kim Jong Un.
Acts of Aggression
Some of North Korea’s attempts against South Korea
Jan. 21, 1968: North Korean commandos reach presidential Blue House in Seoul and attempt to kill President Park Chung-hee. They fail, but kill two South Korean police and five civilians; 28 of the commandos are killed.
Oct. 9, 1983: North Korean agents bomb a meeting attended by President Chun Doo-hwan in Rangoon, Burma, killing three members of his cabinet and 14 others in his entourage.
Nov. 29, 1987: Two North Korean spies place a time bomb on a Korean Air flight from Baghdad to Bangkok; it explodes over the Andaman Sea near Burma, killing 115.
June 16, 1999: North Korean warships accompany fishing boats across the maritime border in the Yellow Sea, leading to a 10-minute gunbattle that resulted in the sinking of a North Korean ship.
June 29, 2002: North Korean warships venture three miles south of the maritime border in the Yellow Sea and skirmish with two South Korean ships; six South Korean sailors are killed.
Nov. 10, 2009: A North Korean warship strays one mile south of the maritime border in the Yellow Sea, leading to a brief gunbattle with two South Korean ships.
There’s less evidence of this possibility, but when Mr. Kim was rising in power in the 1970s and 1980s, North Korean media attributed several military actions to him. His father, North Korean founder Kim Il Sung, was a war hero and resister of Japan’s colonization of the Korean peninsula, which ended after World War II in 1945.
If North Korea is ultimately blamed, South Korean officials don’t expect difficulty building public support to penalize it. North Korea’s military has blamed South Korea for the Cheonan’s sinking, though the North hasn’t explicitly denied being involved.
Should the North be responsible, Seoul would likely ask the U.N. Security Council to create additional economic sanctions that would be binding on all nations, according to a high-ranking South Korean official.
Meanwhile, South Korea would likely end its own remaining economic activities with North Korea. The South Korean official noted that since Mr. Lee took office, Seoul has sharply reduced trade and investment with Pyongyang by tying such activities to a reduction of nuclear-weapons development in the North.
“We can cut the rest off,” the official said, including closing a joint industrial park near the inter-Korean border where South Korean firms employ 40,000 North Koreans.
The government discussion is also influenced by the coming June 2 biennial election of South Korea’s National Assembly.
Opposition lawmakers have focused on the military’s shortcomings in handling the sinking, particularly a slowness early on to provide information.
Members of the ruling conservative party have emphasized the prospect of North Korean involvement and raised questions about the military’s preparedness for surprise attacks.
A finding of Northern aggression might help politicians in the ruling party because it has long taken a harder line with Pyongyang than other parties. Uncertainty will allow politicians in opposition parties to continue criticizing the efficiency of the military and incumbent government.
Lawmakers suspended campaigning until after a Thursday funeral for the sailors, which will cap five days of national mourning that began Sunday. But they plan their own investigation of the sinking afterward with an eye toward finishing before the election.
The main probe is being conducted by 43 civilian and military experts, including some from the U.S., Australia and Sweden. The investigation’s chief, Yoon Duk-yong, said Sunday said the damage to the 1,200-ton ship’s hull makes it “highly likely that a noncontact explosion was the cause.”
Metal fatigue was ruled out because the ship didn’t break cleanly. Mr. Yoon promised further analysis.
There remains a chance the explosion was caused by a mine that South Korea or the U.S. planted along the countries’ shared maritime border 40 years ago, when a nearby island was used as a radar station. Defense officials believe such mines were cleared long ago.
“People in the government are rather cautious until we come up with the decisive material that can verify what was the cause,” says Park Chan-bong, a former negotiator with North Korea for the South Korean government who is now an adviser to the ruling Grand National Party. “Until then, I think it is rather rational to wait.”