The United States flew two B-1 bombers over South Korea yesterday in a show of force against North Korea's latest and most powerful nuclear test last week, while the Obama administration pushes to impose new sanctions on the defiant state.
US President Barack Obama's nuclear envoy, Mr Sung Kim, was in Seoul yesterday for talks with his South Korean counterpart, and said they are working closely with the United Nations and other partners to secure the "strongest possible" measures against North Korea to show Pyongyang that "there are indeed serious consequences for its unlawful and dangerous actions".
Stressing the urgency of the situation, Mr Kim added that they will also work with China, North Korea's only ally, to close any loopholes in the existing UN Security Council Resolution 2270, adopted in March against Pyongyang's fourth nuclear test early this year.
The North has ramped up its nuclear programme in the past eight months, firing 22 ballistic missiles and conducting two nuclear tests. Given the accelerated pace, some experts estimate that the regime may have accumulated enough raw materials to make 20 nuclear bombs by the end of the year.
Pyongyang is now demanding to be recognised as a "legitimate nuclear weapons state", insisting that its missile and nuclear tests are necessary for self-defence against US-led hostile forces.
But Mr Obama and his allies are not backing down from their tough stance against the North. The US Air Force deployed two B-1 bombers from Guam to South Korea's Osan Air Base, 77km from the border, yesterday to demonstrate its "steadfast commitment" to the defence of South Korea, said a statement from US Forces Korea.
General Vincent Brooks of US Forces Korea and General Lee Sun Jin of South Korea's Joint Chiefs of Staff said during a joint press conference that they will continue to prepare themselves against North Korea's "continued aggressive behaviour".
Meanwhile, South Korean President Park Geun Hye has called on the military to "stay fully ready to retaliate" and put an end to the North Korean regime if needed. She also urged opposition leaders to support her decision to deploy the US Terminal High Altitude Area Defence (THAAD) anti-missile system in South Korea and rejected proposals to send a special envoy to Pyongyang to initiate talks.
South Korea and the US have insisted that the North should give up its nuclear weapons before resuming dialogue, but there is speculation that China and Russia might push for talks without pre-conditions.
Mr Kim said dialogue remains a viable option - if the North is ready to commit.
He also refuted critics who questioned the effectiveness of sanctions in changing North Korea's behaviour. He argued that the penalties take time to work and those imposed in March have had some effect in restricting Pyongyang's access to foreign currency already.
"I know there is a lot of frustration that sanctions have not resolved (this issue) immediately, but it's important to note that sanctions need time (to work)," he said.
"It requires a sustained, systematic effort to have the kind of effect we desire."