The existing off-base curfew on U.S. troops stationed in Korea will be modified and extended indefinitely, the commanding unit of the American forces here announced Tuesday.

The U.S. Forces Korea (USFK) announced its commander, Army Gen. James D. Thurman, decided to extend the current curfew "until further notice." It was set to expire this Friday.

"The purpose of the curfew is to ensure continued mission readiness and to assess the current operational environment," the USFK said in a statement. "The new off-installation curfew begins Jan. 7 at 1 a.m. The hours of the curfew are from 1 a.m. to 5 a.m. seven days a week, a modification of the previous policy."

The current curfew is in effect from midnight to 5 a.m. on weekdays and 3 a.m. to 5 a.m. on weekends.

On Oct. 7 last year, Thurman imposed the curfew for 30 days, and extended it again in November. It had been withdrawn in July 2010 after being in place for nine years.

In September and October, two U.S. soldiers came under investigation for separate sexual assault charges and one was sentenced to 10 years in prison. A third U.S. soldier is under suspicion of setting a Seoul pub on fire in November.

Thurman once again stressed combat readiness on Tuesday.

"We must remain focused on our primary mission here, which is to deter against external aggression and if required, defend the Republic of Korea side-by-side with our ROK counterparts," he was quoted as saying, referring to South Korea by its official name. "I anticipate and expect that our service members will continue to maintain the highest standards of individual readiness and professionalism while they serve in the Republic of Korea."

The USFK said the curfew applies to all U.S. service members in Korea, whether permanently assigned here or temporarily. It doesn't cover military officials at the U.S. embassy in Seoul, but military family members of civilians working on base will be "encouraged to abide by this policy," the USFK added.

It said Thurman will continue to monitor and assess the USFK's operational and mission readiness.

About 28,500 U.S. soldiers serve in South Korea. Their presence is a legacy of the 1950-53 Korean War, which ended on an armistice rather than a peace treaty and left the two Koreas technically at war.(Yonhap)