Former top U.S. military commanders in Korea were divided Tuesday over the timing of wartime operational control, while agreeing with the urgency of coping with North Korea's "asymmetric" capabilities. They were united in urging the allies to maintain an effective combined command structure. Retired Gen. John Tilelli said the U.S. government should accept South Korea's request for a further delay in the OPCON transfer, now set for December 2015. Tilelli, who served as head of the U.S. Forces Korea (USFK) from 1996 to 1999, called for a thorough review of South Korea's defense capabilities and North Korea's threats to decide on the appropriate timing. He was speaking at a security forum here, also joined by retired Gen. Walter "Skip" Sharp, who led USFK from 2008 to 2011 and his successor, James D. Thurman. It was unusual for three former USFK chiefs to sit together at a public event. Sharp put more emphasis on South Korea's continued development of its defense capabilities, especially through the modernization of weaponry. In a recent report, he also said the U.S. should transfer wartime OPCON toSouth Korea as scheduled. "It is time for Korea to command the defense of its own country," he said. Thurman did not clarify whether he supports Seoul's request for a delay in the wartime OPCON transition, only emphasizing the importance of a combined command and control system. The former USFK leaders agreed that the Seoul-Washington alliance remains on a right track. But they voiced concerns about a possible negative impact from U.S. budget constraints. They also warned the allies to better prepare for North Korea's nuclear, missile and other "asymmetric" threats. "I think that's probably the greatest threat over there," Thurman said. He said he is not that worried about North Korea's ground forces but its "missile portfolio," including long-range or road-mobile missiles, is very worrisome. "A road-mobile capability is hard to find in a battlefield," he said. North Korea also has a large stockpile of chemical weapons and cyber capability, he said. "So that's what I think we have to worry about for the future," Thurman said. He made clear his opposition to the redeployment of U.S. tactical nuclear weapons to the peninsula. "There is no reason for that," he said, because Washington's commitment provides sufficient capability to defend South Korea. Last year, South Korea's Park Geun-hye administration asked the U.S. to push back the date for handing over the OPCON in the event of war, citing North Korea's growing military threats. Seoul gave its military command to the U.S.-led U.N. forces shortly after the outbreak of the 1950-53 Korean War. It regained peacetime OPCON in 1994. The allies are in consultations over Seoul's request for rescheduling the timing of wartime OPCON transfer.