A spokesman at North Korea's foreign ministry claimed that the ferry service is the outcome of normal economic cooperation between Pyongyang and Russia.

"This is a normal bilateral cooperation work aimed to expand bilateral economic relations and deepen the friendship through humanitarian exchanges and visits," the spokesman was quoted as saying by the Korean Central News Agency.

The spokesman said that the US is seriously encroaching on the legal interests of North Korea and Russia by finding faults with bilateral economic cooperation.

Washington's move is aimed at preventing "the DPRK-Russia economic cooperation and suffocating the DPRK through a tightened economic blockade." he said.

The DPRK refers to the abbreviation of North Korea's full name -- the Democratic People's Republic of Korea.

The operation of the ferry service came amid heightened tensions over North Korea's nuclear and missile development programs.

North Korea is under a set of heavy United Nations Security Council sanctions over its nuke and missile provocations.

The North is seeking to strengthen its ties with Russia as its ties with China, the North's main ally, have been strained over its nuclear arsenal.

The ferry has the capacity to carry up to about 200 passengers and about 1,500 tons of cargo, according to Russia's Tass news agency. It plans to sail four times a month starting Thursday. (Yonhap)