U.S. flexes muscle at North Korea, flying bombers over South Korea: reports

In a show of strength, the U.S. sent two supersonic B-1 Lancer strategic bombers to fly over South Korea on Tuesday as a response to North Korea's fifth nuclear test on last week, the Associated Press and Reuters reported.

An AP photographer spotted the B-1 bombers, escorted by U.S. and South Korean jets, as they flew over the Osan Air Base 75 miles from the North-South border. According to AP, the bombers likely landed in their base in Guam.

The fly-over was scheduled Monday but was delayed due to weather conditions in Guam, Reuters reported.

It's a display of force following North Korea's fifth nuclear test on Friday, AP reported. The test supposedly involved "standardized" warheads, which raised concerns that the North is making progress in its weapons testing program.

U.S. Treasury Secretary Jack Lew said the country would keep pressure on North Korea, South Korea's Yonhap news agency reported.

"They have done more testing both of nuclear weapons and of missiles in recent months in a way that has the world's attention clearly focused, and we will continue to sharpen financial tools as we can," he said. "The goal is to change the policy."