SEOUL, Oct 30 (Reuters) - North Korea's communications ministry was behind a series of cyber attacks against South Korean and U.S. websites in July, the South's spy chief was quoted on Friday as saying.

Dozens of major U.S. and South Korean government and business sites were slowed or disabled with traffic generated by malicious software planted on personal computers unknown to their users.

South Korean officials said at the time that North Korea was a prime suspect. [ID:nSEO117189] [ID:nN08404460]

"The attacks on Korean and U.S. Internet sites were traced back to circuits originating in China," the South's spy chief Won Sei-hoon was quoted as telling a closed-door parliamentary committee meeting by Yonhap news agency.

"North Korea's communications ministry has been confirmed as leasing the line," Won reportedly said.

Some South Korean government websites, including the Defence Ministry and National Intelligence Service, were affected in the wave of attacks that lasted several days but did not lead to a breach of sensitive material or damage to online infrastructure, the agencies said.

Internet access is denied to almost everyone in impoverished North Korea. Intelligence sources say leader Kim Jong-il launched a cyber-warfare unit several years ago.

South Korea's intelligence agency declined to comment on the Yonhap report. (Reporting by Jack Kim; Editing by Alex Richardson)

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