North Korea has completed preparations for another nuclear test, South Korea's Yonhap news agency reported on Monday.
The news agency cited South Korean government sources who said the North may use a previously unused tunnel at its mountainous test site, according to Reuters.
North Korea on Friday carried out its fifth and largest ever nuclear test, saying later it had mastered the ability to mount a warhead on a ballistic missile and ratcheting up a threat that its rivals and the United Nations have been powerless to contain.
"Indications have been gathered that the North has completed preparations to conduct a nuclear test at any time in the third tunnel that has not been used previously," Yonhap quoted one of the government sources as saying in its latest report.
It did not elaborate on what activities had been detected at the Punggye-ri nuclear test site near the North's northeastern shore, the location of its five nuclear explosions.
North Korea said on Sunday a push for further sanctions following its latest nuclear test was "laughable", and vowed to continue to strengthen its nuclear power, according to Reuters.
U.S. President Barack Obama condemned the nuclear test on Friday, calling it a “grave threat” to regional security and international stability and vowing to take “additional significant steps” against the isolated North Korea.
Israel issued a condemnation of the North Korean test as well, with the Foreign Ministry saying it “contradicts international norms and Security Council resolutions.”
“The nuclear test, and the ballistic missile tests that preceded it, necessitate concrete action by the international community against the proliferation to the Middle East carried out by North Korea in a variety of spheres,” said the Israeli Foreign Ministry.
The UN Security Council denounced North Korea's decision to carry out the test and said it would begin work immediately on a resolution. The United States, Britain and France pushed for the 15-member body to impose new sanctions.
The test is the latest in a series of provocations by Pyongyang. Late last month, North Korea fired a submarine-launched ballistic missile (SLBM), which its leader, Kim Jong Un, later boasted was "the greatest success" that put the country in the "front rank" of nuclear military powers.
In July, the North test fired three ballistic missiles. In fact, tensions in the region have soared since Pyongyang carried out its fourth nuclear test in January, claiming it was a hydrogen bomb.