Hours after South Korea’s top diplomat questioned North Korea’s membership of the United Nations, the United States on Wednesday flew two of its supersonic bombers over its ally South Korea for the second time this month in an attempt to apparently deter North Korea’s nuclear ambitions.

Pyongyang conducted its fifth and most powerful nuclear test on Sept. 9, inviting flak from the international community. Kim Jong Un’s regime could conduct another nuclear test soon, South Korea’s Yonhap News Agency reported last week.

After flying two B-1B bombers over South Korea on Sept. 13, the U.S. Forces Korea (USFK) said one of the bombers landed at Osan Air Base, 120 km (75 miles) from the North Korean border.

“What we are showing today is just one tool we have to choose from a wide array of options. The alliance grows stronger every day and we remain prepared to defend and to preserve the security of the Korean Peninsula and the region,” Lt. Gen. Thomas Bergeson, commander of the U.S. 7th Air Force in South Korea, said in a statement, the Associated Press (AP) reported.

Currently, the bombers do not carry nuclear weapons but the AP reported South Korean military analysts saying that they can be reconfigured for nuclear capabilities.

Pyongyang’s reaction to the earlier bomber flights was one of dismissal. A statement from North Korea’s state-run Korean Central News Agency said, “They are bluffing that B-1Bs are enough for fighting an all-out nuclear war.”

“The U.S. imperialists keep letting their nuclear strategic bombers fly over South Korea in a bid to seek an opportunity of mounting a preemptive nuclear attack,” the statement added.

In an attempt to urge strong action from the international community, South Korean Foreign Minister Yun Byung-se said in an interview with the AP late Tuesday on the sidelines of a U.N. gathering in New York, “I think all members of the U.N. have to ask themselves whether North Korea is really qualified as a member of the U.N.”

“This latest test is a very sobering reminder (that) the danger and the threat from North Korea is now reaching a very, very dangerous stage. For many years we have been talking about the development of North Korea's nuclear weapons and missiles, and now we may be reaching a stage where we have to worry about the deployment of nuclear-tipped missiles,” Yun added.