WASHINGTON (REUTERS) - United States Secretary of State John Kerry spoke to South Korean Foreign Minister Yun Byung Se on Wednesday (Jan 6) about North Korea's nuclear test, the US State Department said.

Mr Kerry reiterated the US commitment to South Korea's security and "emphasised the need for a unified international response to the DPRK's provocative actions", the State Department said in a statement.

Mr Kerry also spoke to Japanese Foreign Minister Fumio Kishida on Wednesday and underscored the need for an international response to North Korea's nuclear testing, the State Department said.

"The secretary reiterated the steadfast commitment of the United States to the security of Japan and emphasised the importance of a unified international response to DPRK's (North Korea's) provocative actions," the department said in a statement.