Government prosecutors Thursday arrested two senior officials of Hyundai Engineering and Construction Co. and charged them with paying a group of men to kidnap a labor organizer. The prosecutors said they are trying to determine whether other Hyundai officials were involved in the kidnapping. The organizer was freed after several days when he resigned as an employee of the construction company. Earlier Thursday, about a dozen radical students hurled rocks at the headquarters of the giant Hyundai group in Seoul to protest the kidnapping at the Hyundai subsidiary. No injuries were reported. The arrests and the attack by the students came as labor unrest continued at three other Hyundai plants in southern South Korea. The Hyundai group is one of the largest conglomerates in the nation. In Ulsan, management on Wednesday locked out 20,000 striking workers at Hyundai Motor Co., the nation's largest automaker, and said there was little chance of settling the strike for higher wages. The walkout began Monday. At Hyundai Precision and Industry Co., which makes trains, management and leaders of the 4,000 strikers held two rounds of talks Thursday but failed to end a one-week strike at the company's plants in Ulsan and Changwon. The talks were held one day after strikers freed one of the 11 executives they took hostage on Friday. They were still holding 10 executives on Thursday. Strikers at Hyundai Motors want raises of up to $180 a month, against a company offer of $105. The workers earn an average of $750 after five years. Hyundai Precision on Thursday offered to raise workers' pay $85 a month, but workers stuck to their demand of a $180 increase. They earn $600 a month. ``Punish the masterminds of the kidnapping,'' the students shouted as they hurled rocks at the Hyundai group's main building in Seoul, breaking four windows. The students ran away before police arrived. Several hours after the attack, government prosecutors arrested two Hyundai Engineering officials, executive board member Choi Jae-dong, 47, and manager for general affairs Kang Myung-ku, 42, and charged them with hiring several men to kidnap labor organizer Suh Jung-ui, 34. Suh was kidnapped May 10 by a group of unidentified men as he left a Seoul restaurant where he had met with some officials of the construction company, which is based in Seoul. Suh, who worked at the company's Seoul headquarters, returned home several days later and said he was released after he agreed to write a letter of resignation addressed to the company. Hyundai Engineering denied involvement at the time. Details of the kidnapping emerged this week when some of the alleged kidnappers surrendered to police or were arrested in Seoul and other cities. Their leader told police Hyundai Engineering executives offered him $27,000 to kidnap Suh and persuade him to drop his labor organizing effort.