South Korea and the United States beefed up their joint defense readiness after North Korea claimed Wednesday to have conducted its first successful hydrogen bomb test.
"The allies have increased surveillance activities to monitor the North Korean military," said Defense Ministry spokesman Kim Min-seok during a press briefing. "The military held a teleconference of commanders and shared information on the current situation while enhancing the vigilance posture against North Korea."
"We will take necessary countermeasures against the North's nuclear test under the South Korea-U.S. alliance in cooperation with the international community," he said.
Defense Minister Han Min-koo discussed the situation over the phone with his U.S. counterpart, Ash Carter.
The ministry formed a joint counter-crisis team with the Joint Chiefs of Staff following the detection of seismic activity in North Korea. The military was then put on high alert and surveillance of North Korea strengthened, according to another defense ministry official who asked not to be named.
Joint Chiefs of Staff Chairman Gen. Lee Sun-jin and the commander of the U.S. Forces Korea Gen. Curtis Scaparrotti had a telephone conversation and agreed to ensure "close collaboration" between both countries, the official said.
The U.S. Air Force reportedly sent its WC-135 aircraft from Kadena Air Base in Okinawa to detect any residual radioactivity over the Korean Peninsula.
The aircraft collects samples from the atmosphere for the purpose of detecting and identifying evidence of nuclear explosions. One was dispatched in 2006 and 2009 after North Korea conducted nuclear tests.
A few hours after North Korea claimed it had successfully tested its first hydrogen bomb, the U.S. and Japan condemned the repressive state for violating U.N. resolutions. The United Nations Security Council (UNSC) was scheduled to convene Thursday in response to the situation.
The UNSC is expected by observers to issue a statement denouncing the North's violation of U.N. resolutions and start discussing the imposition of additional sanctions against the isolated nation.
It is inevitable that the international community will conduct strengthened countermeasures against the North's provocation according to previous U.N. resolutions, said observers.
The North's previous nuclear tests in 2006, 2009 and 2013 led to a series of sanctions imposed by the U.N. against the regime in Pyongyang. The latest, passed after the North's nuclear test in February 2013, calls upon member states to inspect North Korean cargo within their territory, and subsequently seize and dispose of items prohibited by previous U.N. resolutions including luxury goods.
China, North Korea's major ally with veto power, is expected to play a key role in deciding the level of sanctions to be imposed, according to observers.
"The content of the sanctions may be similar to previous ones but this time UNSC members are expected to discuss how to exert more pressure when implementing them," said Sheen Seong-ho, a professor at the Graduate School of International Studies at Seoul National University. "It largely depends on China's call but I am sure that Beijing's view will be in tune with the strong opinion of other council members."