SEOUL, Aug 9 (Reuters) - South Korea and the United States will begin preliminary military drills on Tuesday, the Yonhap news agency reported on Monday, despite North Korea"s warning that the exercises would dent signs of an inter-Korean thaw. The drills, called Crisis Management Staff Training, were designed to examine the allies" readiness to respond to a potential contingency, and will be held until Friday before switching to full-scale exercises scheduled for Aug. 16-26, Yonhap said, citing unidentified military and government sources. South Korea"s defence ministry said the timing, scale and formation of the drills were not yet finalised. The U.S. Forces Korea declined to comment, citing its policy. South Korea and the United States regularly stage military exercises, mainly in the spring and summer, but North Korea has for decades reacted angrily, calling them a rehearsal for war. Yonhap said the drills would consist mostly of computerised simulations with no live field training involving U.S.-based troops, in light of the coronavirus pandemic. Kim Yo Jong, the sister of North Korean leader Kim Jong Un and a senior official of the ruling Workers" Party, warned the South last week that holding the drills would undercut efforts to rebuild relations. read more The two Koreas recently restored hotlines that Pyongyang severed a year ago, as Kim and South Korean President Moon Jae-in are seeking to mend strained ties and resume summits. read more The North"s warning had prompted some Seoul officials and members of Moon"s ruling party to call for postponing the exercises to expedite inter-Korean reconciliation. read more But ruling party chief Song Young-gil said on Thursday that the drills cannot be delayed, as they are regularly conducted for defensive purposes and preparations were "almost complete." The exercises had been scaled back in recent years to facilitate talks aimed at dismantling Pyongyang"s nuclear and missile programmes in return for U.S. sanctions relief. But the negotiations collapsed following a failed second summit in 2019 between Kim and then U.S. President Donald Trump.