US airmen assigned to South Korea are banned from buying or drinking alcohol during their first 30 days in the country under a new rule underscoring the "serious mission" the troops face, officials said Friday.

The program is meant to promote "mission readiness" as well as "safety, health, welfare, good order and discipline," spokesman Captain Ray Geoffroy told AFP.

The rule is part of a "Korean Readiness Orientation" program for incoming troops issued by the 7th Air Force commander, Lieutenant General Jan-Marc Jouas.

"Airmen must understand the threat when they come here," Jouas said in a statement.

"We have a serious mission with a serious enemy, and we must be ready to contend with that by utilizing personal resiliency and a readiness orientation program," he added.

"Airmen assigned to Korea must understand what it means to be ready to fight tonight and why we must be ready."

The rules come amid concern over alcohol-fueled sexual assaults in the military as well as persistent worries over North Korea, which has conducted half-a-dozen missile, rocket and heavy artillery tests over the past month.

The new policy, which took effect his month, includes a daily curfew of 10 pm to 5 am, training for sexual assault prevention and "alcohol awareness," the Air Force said.

The orientation also strongly recommends that arriving airmen tour the demilitarized zone that separates South and North Korea.

"We are guests here and not only do our actions matter, they have strategic implications," Jouas said. "This is a fresh start to change the tone in Korea and leave a culture that is better than how we found it."

The policy was aimed at conveying to troops that times had changed and that South Korea should not be seen as an opportunity for drunken nights and visits to brothel bars, officials said.

In the past, numerous bars outside US bases were linked to prostitution rings but restrictions on troops have reduced the number of those establishments in recent years, Jouas told the Air Force Times.