North Korea denied an allegation Thursday that it had hacked into a Seoul subway operator last year, calling South Korea's accusation against it a childish political plot.

The North is suspected of launching a cyber attack on two operating servers of Seoul Metro, which runs four major subway lines, for at least five months in 2014, according to a lawmaker from the ruling Saenuri Party. 

North Korea's key propaganda website, Uriminjokkiri, warned that South Korea will face a bigger backlash if it continues to make groundless claims.

"Whenever cyber attacks occur, South Korea blindly criticizes us without presenting any proof," the North said. "It is South Korea's bad practice that whenever (political) crisis crops up, it cooks up a conspiracy blamed on us."

South Korea's intelligence agency said that the hacking tactics coincided with those of cyber attacks that took place in 2013 by North Korea on South Korean financial firms and TV broadcasters.

Seoul Metro has been suffering from a series of cyber attacks.

More than 35,000 attacks have taken place so far this year, nearly matching over 37,700 cases reported last year. (Yonhap)