South Korea's audit agency told the defense minister to punish 25 top military officials for failing to ensure combat readiness ahead of the deadly sinking of a South Korean warship blamed on North Korea, an official said Thursday, according to AP. A team of international investigators concluded last month that a torpedo from a North Korean submarine tore apart and sank the vessel near the two Koreas' disputed sea border on March 26, killing 46 South Korean sailors. It was one of South Korea's worst military disasters since the 1950-53 Korean War. The Board of Audit and Inspection said Thursday it told Defense Minister Kim Tae-young a day earlier to «take appropriate steps, including disciplinary action» against the chairman of the Joint Chiefs of Staff, 22 other senior officers and two civilian ministry officials for negligence. Park Soo-won, a senior BAI official, said that the military had expected that a North Korean submarine or submersible vessel could secretly attack a South Korean ship near the sea border following a naval skirmish in November that left one North Korean soldier dead and three others wounded. However, the navy and the Joint Chiefs of Staff did not take appropriate countermeasures and neglected combat readiness, Park said. The audit agency also blamed the military for delaying its first report on the incident to the Joint Chiefs of Staff, its chairman and the defense minister. The military also did not correctly relay information to its higher commands, the agency said. The announcement, part of an interim report, came days after North Korea sent the U.N. Security Council a letter warning the world body not to open debate on the Cheonan's sinking. South Korea last week officially asked the Security Council to punish North Korea. North Korea denies responsibility for the sinking and says any punishment would trigger war. Sin Son Ho _ North Korea's permanent representative at the U.N. _ sent Security Council president Claude Heller a letter Tuesday saying the council must not open a debate on the «the unilaterally forged» investigation results because that would infringe upon the North's sovereignty, the official Korean Central News Agency said Wednesday. Sin said the Security Council instead should take steps to get South Korea and the U.S. accept North Korean inspectors to verify the investigation results, it said. Separately, about 300 activists and defectors opposed to North Korea's government gathered in the city of Paju near the inter-Korean border Thursday to denounce leader Kim Jong Il and launch leaflets and DVDs via huge balloons across the border. The leaflets and the DVDs contained information on the sinking of the South Korean ship, said Choi Sung-yong, one of the protest organizers. The activists said the balloons carried 150,000 leaflets, 300 DVDs, 200 portable radios as well as $2,000 in cash to support North Koreans. Park Sang-hak, who heads a group of North Korean defectors, said the activists wanted to «let North Koreans know the truth» about the ship sinking. «What a weak, opportunistic government we have in South Korea,» Park said. «The government should be sending these flyers.» South Korea late last month announced a series of steps to punish the North, including curtailing trade and resuming propaganda operations. The government resumed radio broadcasts into the North, but has so far stopped short of sending leaflets or starting broadcasts via loudspeaker across the border.