London Olympic organizers have apologized to North Korea after mistakenly displaying South Korea's flag before a women's soccer match.

North Korea refused to take the field after the error, delaying the start of their match Wednesday against Colombia by more than an hour. The North Korean team went on to win 2-0.

Organizers said they will take steps to ensure that type of mistake does not happen again.

In other action, the defending gold medalist United States came back from behind to beat France 4-2. Britain beat New Zealand 1-0.

Men's soccer teams also play Thursday. Opening ceremonies for the Olympics are Friday.

On the eve of the opening, British Prime Minister David Cameron said his biggest concern is a “safe and secure” Olympics.

Meanwhile, the International Association of Athletics' Federations suspended nine track and field athletes for doping violations, in a crackdown on the use of prohibited substances leading up to the Olympics.

More than 10,000 athletes are competing in 26 sports at the Olympics. The competition runs until August 12.