North Korea on Thursday reiterated its pledge to bolster its nuclear deterrence both in quality and quantity against what it called U.S. hostile acts, the country's state-run media said.

North Korea defended its latest test of intermediate range missiles, saying that it is natural for the country to take steps to boost nuclear deterrence to counter Washington's constant threats, according to the Korean Central News Agency.

North Korea "will continue taking a series of steps for bolstering up the nuclear deterrent for self-defense both in quality and quantity to cope with the ever-escalating U.S. hostile acts against the former," a spokesman at the foreign ministry was quoted as saying by the KCNA.

Pyongyang claims that the U.S. constantly poses a nuclear threat to the North, saying that Washington brought strategic assets including nuclear-powered submarine Mississippi and B-52H strategic bombers to the Korean Peninsula.

Last week, the North fired off two Musudan mid-range ballistic missiles, marking its fifth and sixth launch since April. It claimed to have carried out the successful launch of what it called the Hwasong-10 missile, saying that it has the capacity to strike U.S. forces in the Pacific region.

The North's latest move raises concerns about an advance in the country's nuclear and missile capabilities. Pyongyang is seeking to develop a nuclear-tipped intercontinental ballistic missile capable of hitting targets in the U.S. mainland.

The North is banned from using ballistic missile technology under a set of relevant U.N. Security Council resolutions. (Yonhap)