A 171-strong Swiss company got two kilometres into its neighbour before realising the mistake and heading back.

Liechtenstein authorities made light of the intrusion, saying they only knew about it when the Swiss told them.

In 1985, the Swiss had to pay Liechtenstein compensation when rockets fired by its army went astray and set a forest ablaze.

'All so dark'

The latest incident began on Wednesday night during a routine training exercise for the infantrymen in the Alpine forests close to an unmarked section of the border.

The company commander led his men in the wrong direction in bad weather but gave the immediate order to return when realising the error.

"It was all so dark," one soldier told the Swiss newspaper Blick.

A spokesman for the Liechtenstein authorities said: "It's not like they invaded with attack helicopters."

The BBC's Paul Legg says the incident is embarrassing for the Swiss but not as bad as the one in 1985.

The countries became embroiled in a lengthy dispute when the protected forest was set on fire.