Seoul is being careful to not appear as if it is jumping to conclusions. But on Friday the leader of an official investigation into the incident said the vessel most likely was sunk by an external explosion, as opposed to the explosion of its own ammunition or fuel.
The Cheonan blew up and split in two on March 26 during a routine mission near the maritime border with North Korea. The disaster killed at least 36 sailors and has thrown South Korea into mourning.
It would not be surprising if many South Koreans blame their northern neighbor for the incident. In the 57 years since an armistice halted the Korean War, the insular North Korean regime has carried out numerous provocations against the south, including armed assaults, kidnappings, and assassination attempts.
The most intense phase of such activity occurred during the late 1960s, notes a Congressional Research Service report on the subject. For instance, Pyongyang infiltrated some 740 armed agents into the south in 1967 and 1968 alone.
Here is a list of some of the most serious North Korean incidents, as compiled by US congressional researchers [PDF]:
•"In 1968, a 31-member North Korean commando team infiltrated into Seoul in an attempt to assassinate President Park Chung Hee. Before they reached Park’s office complex they were intercepted, and most killed, by South Korean police."
•"In 1974, a North Korean agent sneaked into South Korea from Japan and fired shots at President Park during a public function. Park escaped unhurt, but his wife was hit by stray bullets and died shortly thereafter."
•"In 1978, a South Korean actress and her film director husband were kidnapped in Hong Kong and taken to Pyongyang, where they were put to work making propaganda films for the North Korean leadership. The couple escaped in 1986 while filming in Vienna."
•"In 1983, a powerful bomb exploded at a memorial in Burma minutes before South Korean President Chun Doo Hwan was due to arrive for a wreath-laying ceremony. Seventeen other South Korean officials were killed. Two North Koreans charged in the incident were convicted in Burmese courts and later executed."
•"In 1987 North Korean agents planted a bomb on a Korean Airlines jet scheduled to fly from Baghdad to Seoul. It exploded in midair, destroying the plane and all aboard. Reportedly the attack was meant to warn nations against participating in the Seoul Olympics."
•"In 1996 a North Korean submarine landed 26 agents on South Korea’s east coast. Most were captured or killed."
•"In 1997 three North Korean patrol boats slipped into South Korean waters south of the maritime border and opened fire on South Korean patrol
•"In 1998 a North Korean midget sub became entangled in a South Korean fishing net. When brought to shore, the crew was found to have committed mass suicide."
•"In 1999 North and South Korean naval vessels clashed in a nine-day confrontation over disputed waters in the Yellow Sea. An exchange of fire sank one North Korean patrol boat and damaged several South Korean boats."
•"In 2002 another Yellow Sea battle led to the sinking of a South Korean navy vessel, killing six."