Trains from North and South Korea will pierce their heavily armed border on Thursday, restoring for the first time an artery severed in their 1950-1953 war and rekindling dreams of unification.

It has taken the two Koreas 56 years to send trains -- one starting in the South and one in the North -- across the Cold War's last frontier for the planned runs of about 25 km (15 miles).

The two passenger trains, carrying 100 South Koreans and 50 North Koreans each, are scheduled to cross the border at just after 0300 GMT and then head back later in the day.

Elaborate ceremonies have been planned for the trains' departures and highly symbolic arrivals at stations a few kilometers (miles) on the other side of the border.

North Korea's military, fearful of increased openings between the isolated country and the outside world, cancelled a planned run a year ago. It agreed last week to a one-off run, despite pressure from Seoul for more crossings.

The South Korean government has been criticized at home for sending massive aid to the North only to see its largesse rebuffed by Pyongyang, which has halted cooperation projects and sparked a security crisis with a nuclear test last year.

South Korea, fearful of the hundreds of billions of dollars it would cost to unify with its impoverished neighbor, has sought a series of projects to gradually bring the two together.