SEOUL, Aug 10 (Reuters) - North Korea did not answer routine calls on inter-Korean hotlines on Tuesday, South Korea said, hours after a senior official in Pyongyang warned Seoul and Washington over annual joint military drills set to begin this week. Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, accused South Korea of "perfidious behaviour" for going ahead with the drills after North Korea agreed to restore the hotlines in late July, having cut them last year amid rising tensions. read more Kim said U.S. military actions showed Washington"s talk of diplomacy was a hypocritical cover for aggression and that peace would only be possible if it dismantled its military force in the South. In statement carried by North Korea"s state news agency, she called the exercises an "act of self-destruction for which a dear price should be paid as they threaten the safety of our people and further imperil the situation on the Korean peninsula". South Korea and the United States are set to hold computer-simulated exercises next week, but preliminary training began on Tuesday, military sources told Reuters. read more The two Koreas typically check in over the hotlines twice a day, and North Korean officials answered morning calls as usual on hotlines maintained by South Korea"s military and those used by the unification ministry, which handles relations with Pyongyang. But the South"s calls in the late afternoon were unanswered, the unification and defence ministries said. U.S. State Department spokesman Ned Price said he had no specific response to Kim Yo Jong"s remarks when asked about them at a regular briefing, but stressed that the drills were "purely defensive in nature" and Washington "harbors no hostile intent towards" North Korea. Price also reiterated that Washington supports inter-Korean dialogue and engagement and would continue to work with Seoul towards that end. Members of South Korea and U.S. Special forces take part in a joint military exercise conducted by South Korean and U.S. special forces troops at Gunsan Air Force base in Gunsan, South Korea, November 14, 2019. Photo taken November 14, 2019. Capt. David J. Murphy/U.S. Air Force/DVIDS/Handout via REUTERS A North Korea flag flutters next to concertina wire at the North Korean embassy in Kuala Lumpur, Malaysia March 9, 2017. REUTERS/Edgar Su Members of South Korea and U.S. Special forces take part in a joint military exercise conducted by South Korean and U.S. special forces troops at Gunsan Air Force base in Gunsan, South Korea, November 14, 2019. Photo taken November 14, 2019. Capt. David J. Murphy/U.S. Air Force/DVIDS/Handout via REUTERS 1/2 A North Korea flag flutters next to concertina wire at the North Korean embassy in Kuala Lumpur, Malaysia March 9, 2017. REUTERS/Edgar Su A Pentagon spokesman, Martin Meiners, said "combined training events" were a bilateral decision with Seoul "and any decisions will be a mutual agreement." Seoul"s defence ministry declined to comment on the preliminary drills and said the two countries were still discussing the timing, scale and method of the regular exercises. South Korea"s unification ministry said it would not speculate on North Korea"s intentions but would prepare for all possibilities. The United States has kept around 28,500 troops in South Korea - a legacy of the 1950-1953 Korean War, which ended in an armistice rather than a peace deal, leaving the peninsula in a technical state of war. Joint military exercises were scaled back in recent years to facilitate talks aimed at persuading Pyongyang to dismantle its nuclear and missile programmes in return for sanctions relief. But the negotiations collapsed in 2019, and while both North Korea and the United States say they are open to diplomacy, both also say it is up to the other side to take action. Kim Yo Jong vowed that North Korea would boost its "deterrent of absolute capacity", including for a "powerful preemptive strike", to counter the ever-increasing U.S. military threat. Yang Moo-jin, a professor at the University of North Korean Studies in Seoul, said Pyongyang might be positioning ahead of future talks with South Korea and the United States. "Though (Kim) mentioned "perfidious behaviour," her tone seemed relatively restrained as she didn"t threaten specific actions they might take, unlike in the past," he said.