Seoul, Aug 31: The US and South Korea concluded their annual joint military drill, the Ulchi Freedom Guardian, on Thursday amid heightened tension on the Korean peninsula. This year 50,000 South Korean soldiers participated in the drill - that began on August 21 - along with 17,500 US soldiers (3,000 of whom are stationed outside South Korea), 7,500 less than in 2016, reports Efe news. Representatives from seven countries -- Australia, Canada, the UK, New Zealand, Netherlands, Denmark and Colombia -- also participated in the drill that was the largest computerised war simulation in the world. The drill this year focused on the launch of the OPLAN 5015 programme which simulates the destruction of weapons of mass destruction and preparation of troops for a pre-emptive strike. Several senior US army officials oversaw the exercises, including US Pacific Command Commander Admiral Harry Harris, US Strategic Command Commander John E. Hyten and director of the Missile Defence Agency, Lt. General Samuel A. Greaves. Despite the small presence of US troops and absence of large strategic assets such as long-range bombers or aircraft carrier UFG fleet, North Korea vehemently protested against the drills. Pyongyang's Tuesday missile launch was a warning for the US and "significant prelude to the containment of Guam"- the Pacific island which serves as headquarters of major US military bases. On August 26, North Korea broke a month-long arms truce by launching three short-range missiles that re-escalated tension on the Korean Peninsula.