Sri Lanka, Aug. 11 -- South Korea's military has shrunk to about 450,000 people - a decline of 20% over the last six years, according to a defence ministry report released by a ruling party lawmaker on Sunday.

Authorities say the main reason behind the decline is the country's dismal birth rate, which at 0.75 babies per woman is the world's lowest.

South Korea retains compulsory military service mainly because the country is still technically at war with its nuclear-armed neighbour North Korea.

A study published by South Korean researchers in July had suggested that the country would need at least 500,000 soldiers to defend against an attack from the North, which is believed to have 1.3 million active-duty members.

The difference in m...