By Vincent Fribault

LONDON (Reuters) - North Korea's representative at the International Olympic Committee expressed anger and frustration on Thursday at a diplomatic blunder that marred the opening day of the women's Olympic football tournament.

Hours after the tournament got the sporting action underway on Wednesday, the North Korean women's soccer team walked off the field of play after the flag of long-time rival South Korea was mistakenly displayed on stadium video screens.

"Of course the people are angry," North Korea's IOC member Ung Chang told Reuters Television in London.

"If your athlete got a gold medal and put the flag probably of some other country, what happens?"

North and South Korea are divided by the world's most militarized border and remain technically at war after an armistice stopped the Korean conflict in 1953.

The world's most reclusive state, North Korea has few friends in the world beside China, its backer in the Korean War, and is locked in a stand-off with the West over its nuclear weapons programme.

Its relations with its much more prosperous neighbor to the south have vacillated over the decades.

The blunder heaps extra attention on next week's sporting line-up when the men's table tennis tournament pitches 11th seeded North Korea versus second seeds South Korea in the men's team event.

Chang said he had asked for a system to be put in place to prevent further problems.

"It's a very, very essential protocol obligation," he said.

Earlier, the president of the IOC said the mix-up was the result of a "simple human mistake" and that corrective action had already been taken by the London Organising Committee of the Olympic Games.

But with one day left to go before the Olympics officially open, the incident adds another headache for the Games' embattled organizers, already under fire over security, transport and ticketing problems.

(Writing by William James and Sonya Hepinstall/editing by Alan Baldwin)