North Korea lambasted the United States on Thursday for growing calls there to re-list the communist country as a sponsor of terrorism, vowing to bolster its nuclear deterrence.

The U.S. conservatives "intend to brand the DPRK a 'sponsor of terrorism' though its nuclear issue is absolutely irrelevant to terrorism," an unidentified spokesman for the North's foreign ministry was quoted as saying by the country's official Korea Central News Agency (KCNA). 

The DPRK is the acronym of the North's official name, the Democratic People's Republic of Korea.

While stressing that it "will remain unchanged in its principled stand of opposing all forms of terrorism," the North threatened to "bolster its nuclear deterrent at a speed baffling the imagination of the U.S." to counter "hostile policy" toward it. 

Pyongyang was put on the U.S. terrorism sponsor list for the 1987 midair bombing of a Korean Air flight that killed all 115 people aboard. But the administration of former President George W. 

Bush de-listed it in 2008 in exchange for progress in denuclearization talks.

Calls grew early this year for putting the North back on the list after the FBI determined the regime was responsible for the cyber-attack on Sony Pictures, though the U.S. left Pyongyang off the list in its annual terrorism report issued in June, saying Pyongyang is not known to have sponsored any terrorist acts since the plane bombing. (Yonhap)