By NBF News
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After examining the bow of the ship, salvaged on Saturday, officials say the warship was damaged by a “bubble jet” caused by an external underwater blast.

Analysts say that such an effect could be caused by a torpedo or a mine exploding below the ship.

An explosion split the Cheonan in half and it sank, leaving 46 sailors dead.

The ship's sinking has fuelled tensions with North Korea, who many South Koreans believe was responsible for the sinking.

South Korea's government has so far taken care not to directly accuse the North.

“Instead of being directly hit by a torpedo or other underwater weapon, the Cheonan was affected by a strong explosion that occurred below its bottom at a close range,” an official quoted by South Korea's Yonhap news agency said.

South Korean Defence Minister Kim Tae-young said that although the bubble jet effect is the most likely explanation “the possibility of other causes is still under investigation.”

The minister said it would take about a month for the investigation team to come up with the final results of its inquiry.

On Saturday the front half of the Cheonan, a 1,200-tonne corvette, was salvaged by a giant crane for inspection.

Fifty-eight sailors were rescued after the explosion on 26 March.

Tensions mounting
An earlier investigation has already concluded that the explosion which sank the ship was external, fuelling suspicions North Korea may have been involved.

South Korea has avoided blaming the North outright and Pyongyang has denied any role in the sinking of the vessel.

But tensions have mounted over the incident, with Pyongyang accusing Seoul of “deliberately linking” it to the sinking.

South Korean President Lee Myung-bak has vowed to respond “resolutely” to the sinking and bolster the military, though he has not accused North Korea.

The two countries are still technically at war since the 1950-53 war ended without a peace treaty. There have been three previous naval clashes in the same area as the Cheonan went down, off the west coast of the peninsula.