"We strongly urge the DPRK to honor its commitment to denuclearization, and to cease any action that may deteriorate the situation," Foreign Ministry spokeswoman Hua Chunying said.
President Park Geun-hye vowed a tough response to DPRK's bomb test. She said the government "must get the DPRK to face corresponding measures based on close cooperation with the international community".
Foreign Ministry said it hasn't been confirmed that the DPRK has carried out an actual nuclear test. The ministry called on "all interested sides to preserve maximum restraint and to not take actions that could rouse the uncontrolled growth of tensions in Northeast Asia".
Prime Minister Shinzo Abe said the DPRK announcement of a hydrogen bomb test is a threat to his nation's safety. "We absolutely cannot allow this, and condemn it strongly."
The EU foreign policy chief Federica Mogherini said the DPRK's nuclear test, if confirmed, would represent "a grave violation of the DPRK's international obligations not to produce or test nuclear weapons".
President Francois Hollande said "France condemns this unacceptable violation of Security Council resolutions and called for a strong reaction from the international community".