South Korean media continued to speculate Thursday about what caused the Cheonan warship to sink near the border with North Korea last week, as authorities called off efforts to find missing sailors for a second day due to weather.

Some reports cited satellite footage of a North Korean submarine disappearing and then reappearing around the time the Cheonan sunk last Friday as possible evidence of the North's involvement.

Officials, however, said the activity was normal. High-ranking military officials also dismissed as "unfounded" a claim by the head of parliament's defense committee that four North Korean semi-submersibles had crossed into South Korean territory, reports the Chosun Ilbo, a major daily.

The Kyunghyang Sinmun, an influential liberal newspaper, quoted experts raising the possibility that structural "fatigue failure" caused the ship to split in two. An explosion powerful enough to halve the 1,200 ton Cheonan would have been extremely loud, but no such sound was heard by guards or residents near the coast, the paper said.