"The North is targeting South Korea, the weakest node in the international sanctions regime, and trying to break maritime military cooperation among South Korea, the United States and Japan," Choung Tae-ok, the party's spokesman, said in a commentary.

"The decision to allow the entry of Mangyongbong amounts to overlooking (North Korean leader) Kim Jong-un's explicit strategy to make a precedent of a maritime travel exception," he added.

Conservatives here argue that the entry of the North's ferry is yet another attempt at weakening the brunt of international sanctions that have worsened its economic hardships in a way that could endanger the legitimacy of the dictatorial regime. They also said it could cause a fissure in the South Korea-US alliance given that Washington maintains a tough stance on the wayward regime.

"North Korea will continue to provoke and test South Korea," Choung said. "Will the government make another exception based on the Olympic spirit?"

The main opposition party also demanded that the Seoul government respond sternly to the North's reported plan to hold a massive military parade on the eve of the Olympic Games.

Pyongyang is expected to hold a parade on Thursday to mark the 70th founding anniversary of its armed forces. Observers said the event would be used to highlight its military might through a showcase of long-range missiles, warplanes and goose-stepping troops. (Yonhap)