SEOUL (Reuters) - South Korea said on Thursday it suspected North Korea of hacking a South Korean online shopping site and stealing personal records of more than 10 million shoppers in what appeared to be the latest case of a cyber attack by the isolated state.

The South's national police agency said it had traced the data breach to North Korea's spy agency, and it had detected the same IP addresses and codes similar to ones it had used in previous attacks.

South Korea has been on heightened alert against cyber attacks by North Korea since the North conducted its fourth nuclear test in January and launched a long-range rocket the next month, triggering new U.N. sanctions.

North and South Korea have been in a technical state of war since the 1950-53 Korean War ended in an armed truce.

Besides North Korea's nuclear and rocket programs, South Korea says the North has an effective cyber army that has launched a series of attacks in the past three years.

North Korea has denied wrongdoing.

Online shopping operator Interpark Corp said the hacking occurred in May. A hacker had sent emails demanding money in bitcoin virtual currency after the attack, it said.

Interpark said it had been cooperating with the police and no payoff was made.

The hacker used expressions commonly used in the North but almost never said in the South in emails to the company, police said.

"We are sorry that it has become difficult to arrest a suspect as it has been found to be North Korea's conduct," the company said in a statement.

Its shares have fallen 6 percent since news of the data breach broke on Monday.

South Korea has been scrambling to meet what it sees as a rising threat of cyber attack by the North.

In June, police said the North hacked into more than 140,000 computers at 160 South Korean companies and government agencies, planting malicious code as part of a long-term plan to lay the groundwork for a massive cyber attack on its rival.

(Reporting by Ju-min Park; editing by Robert Birsel)