North Korea vowed to continue to strengthen its nuclear program on Sunday calling international pressure for further sanctions following its fifth and biggest nuclear test "laughable".

The isolated dictatorship set off its most powerful nuclear test explosion to date on Friday (9 September), saying it had mastered the ability to mount a warhead on a ballistic missile, to the alarm of the international peacekeeping community.

The US threatened unilateral sanctions on Sunday following a US special envoy meeting with Japanese officials in the wake of the test.

According to state-run news agency KCNA, a North Korean foreign ministry spokesman said in a statement on Sunday (11 September): "The Obama administration running around and talking about meaningless sanctions until today is highly laughable, when their 'strategic patience' policy is completely worn out and they are close to packing up to move out.

"As we've made clear, we will continue to strengthen our nuclear power in quality and quantity to protect our dignity and the right to live as well as to ensure genuine peace from the increasing threat of a nuclear war from the United States."

South Korea condemned the pariah state's actions, and said on 10 September that the latest test showed North Korea's nuclear capability was expanding quickly and that North Korean leader Kim Jong Un was unwilling to alter course.

The UN Security Council denounced North Korea's decision to carry out the test and said it would work immediately on a resolution.

The US, Britain and France pushed for the 15-member body to impose new sanctions.

Punishment for North Korea due

After speaking by telephone with South Korean President Park Geun-hye and with Japanese Prime Minister Shinzo Abe on Friday, Obama said they agreed to work with the Security Council and other powers to vigorously enforce existing measures and to take "additional significant steps, including new sanctions".

"We will be working very closely in the Security Council and beyond to come up with the strongest possible measure against North Korea's latest actions," said US envoy Kim on Sunday.

"In addition to action in the Security Council, both the U.S. and Japan, together with the Republic of Korea, will be looking at unilateral measures, as well as bilateral measures, as well as possible trilateral cooperation," he said, referring to South Korea by its official name.

North Korea
North Korean leader Kim Jong-Un Reuters