South Korea's military shrank by 20% in the past six years to 450,000 troops, largely due to a sharp drop in the population of males of enlistment age for mandatory service in the country with the world's lowest birthrate, a report said on Sunday, Reuters reported.

The dramatic decline in the pool of available males for military service is also causing a shortfall in the number of officers and could result in operational difficulty if it continues, the defence ministry said in the report.

The report was made to the ruling Democratic Party member of parliament Choo Mi-ae, whose office released it.

South Korea's military has steadily declined since the early 2000s when it had about 690,000 soldiers. The pace accelerated during the late 2010s and there were about 563,000 active-duty soldiers and officers in 2019, according to Reuters.