North Korea threatened Wednesday to strengthen its nuclear deterrent as it accused the United States of plotting a preemptive strike against Pyongyang.

"We will further bolster up in quality and quantity the nuclear deterrence for self-defense in face of the U.S. reckless war moves," an unidentified spokesman of North Korea's Foreign Ministry said in English-language comments carried by the North's official Korean Central News Agency.

He also warned that North Korea will "foil any slightest military provocation of the enemies with the Korean-style mode of merciless counteraction."

North Korea has long used the term, "nuclear deterrent," to refer to its nuclear arsenal. North Korea has so far conducted four nuclear tests, including the recent one in January.

The latest warning came in response to what the spokesman says is a provocative report on the North Korea's nuclear issue by a U.S. strategic information consulting company.

The report envisages a "precision air raid operation" against nuclear and military facilities in North Korea to destroy its nuclear capabilities, the KCNA said, without naming the U.S. firm.

The spokesman also claimed that the report is clear proof of the fact that "the surprise preemptive attack and armed invasion against North Korea are in the full-dress process of examination and preparation."

North Korea has frequently accused the U.S. of harboring a hostile policy toward Pyongyang and plotting with South Korea to invade the North, a charge denied by Washington.

Tensions persist on the Korean Peninsula over North Korea's missile and nuclear weapons programs.

Separately, the North's Foreign Ministry sent a letter to the U.N. Secretariat earlier this week and said that the U.N. should not put pressure on North Korea.

The U.N. has imposed the toughest sanctions ever on North Korea over its fourth nuclear test and its long-range rocket launch earlier this year.

The ministry also said the U.N. should exercise its influence on the U.S. so that Washington may give up its hostile policy against Pyongyang.

"We hope that leading figures of the U.N. Secretariat including the Secretary-General would be recorded ... for their positive contribution to easing tension on the Korean peninsula," according to the letter carried by KCNA.

In late May, U.N. Secretary-General Ban Ki-moon urged North Korea to halt provocative actions after Pyongyang carried out an intermediate-range ballistic missile test in violation of U.N. resolutions.

In Honolulu, Rear Adm. Mark Montgomery, director for operations at the U.S Pacific Command, said North Korea has demonstrated the level of missile and rocket engine technology with which it could launch a projectile into space.

He made the comments when asked by a South Korean reporter about the threat posed by North Korea's missile capabilities. (Yonhap)