The Republic of Korea's Foreign Minister Yun Byung-se and US Secretary of State John Kerry (R) shake hands after speaking to reporters at the State Department in Washington, Jan 7, 2014. [Photo/Agencies]

WASHINGTON - Top diplomats from the United States and the Republic of Korea vowed Tuesday to face any threat or provocation by the Democratic People's Republic of Korea, as the Pentagon sent more troops to the ROK.

"We were deeply focused on the challenge of North Korea, particularly with the events that have taken place in recent weeks in North Korea," Secretary of State John Kerry told reporters after meeting with his South Korean counterpart Yun Byung-Se at the State Department.

Kerry reaffirmed US commitment to the defense of its ally, adding "we will continue to modernize our capabilities so that we are prepared to face any threat".

Kerry urged Pyongyang to denuclearize, saying Washington and Seoul "stand very firmly united" on the issue.

He reiterated that "we will not accept North Korea as a nuclear state, nor as a nuclear armed state".

For his part, Yun said that South Korea and the United States will firmly respond based on their robust combined defense posture.

"In addition to our actions, we'll ensure that the UN Security Council will take prompt measures which it deems necessary," he added.

The Pentagon announced Tuesday that it would send 800 soldiers to Camps Hovey and Stanley near the demarcation line with the DPRK on Feb 1, in support of the US forces already stationed in the ROK, which number around 28,500.

The battalion will return to Fort Hood, Texas, after completing its 9-month rotation, but will leave behind its wheeled and tracked vehicles "for use by follow-on rotations," the Pentagon said in a statement.

Yun met with US Defense Secretary Chuck Hagel on Monday and both sides pledged to maintain a robust combined defense as a deterrent against "provocations" by the DPRK.