SEOUL (Reuters) - North Korea's foreign minister said on Tuesday that whether it conducted another nuclear test depended on the behavior of the United States, South Korea's Yonhap news agency reported.

The minister, Ri Yong Ho, said, however, that the United States had destroyed the possibility of a nuclear-free Korean peninsula.

North Korea conducted its fourth nuclear test in January, triggering tough new international sanctions. South Korean officials and experts believe it can conduct a fifth test at any time.

"Any additional nuclear test depends on the position of the United States," Yonhap quoted Ri as telling reporters on the sidelines of a meeting of the Association of South East Asian Nations (ASEAN) in Laos.

Ri added that North Korea was a responsible nuclear state and repeated its position that it would not use atomic arms unless threatened.

"We will not recklessly resort to its use in the absence of substantive threat, unless we are threatened by invasion by another nuclear-power state," he said.

A spokeswoman for the U.S. State Department, Elizabeth Trudeau, repeated a U.S. call for North Korea to take "concrete steps" to meet its international obligations - a reference to its past commitments to abandon its nuclear-weapons program.

"We call on North Korea to refrain from actions and rhetoric that further destabilize the region," she added at a regular briefing when asked about Ri's comments.

Ri said North Korean leader Kim Jong Un had called for a peace treaty with the United States to replace the armistice at the end of the 1950-53 Korean War and the removal of all U.S. troops and equipment from the South.

"This, we believe, is the only way," Yonhap quoted him as saying.

In earlier remarks to the ASEAN conference, Ri said North Korea had made "an inevitable strategic decision that there is no other option but facing with nuclear deterrent the never ending nuclear blackmails of the U.S."

North Korea has responded to the latest sanctions with defiance, conducting a series of rocket and missile tests in spite of repeated international condemnation.

(Reporting by Jack Kim and James Pearson in Seoul, Simon Webb in Vientiane and David Brunnstrom in Washington; Editing by Jeremy Gaunt and James Dalgleish)