Several South Korean websites that specialize in reporting on North Korean issues were hit by cyber attackers on Tuesday, they said late the same day.

Daily NK and Free North Korea Radio both confirmed the attacks in articles posted on their sites. They were said to begin at 2pm local time (0500 UTC) and resulted in the sites being unavailable for some time.

“The attack was aimed at databases and was designed to blow away the entire system. Based on this, we can say that their target was clearly pre-ordained and the aim was to completely incapacitate it,” the Daily NK said in an article on its site.

Access to both sites has since been restored.

The Daily NK also reported that the websites of NKnet and NK Intellectuals Solidarity were also attacked. The former is currently online but the latter cannot be accessed.

The attacks came on the third anniversary of the sinking of the South Korean corvette Cheonan. The ship broke in two and sank near the maritime border with North Korea causing the deaths of 40 sailors and leaving six missing and presumed dead. North Korea denied involvement but an international investigation said the Cheonan sank after being hit with a torpedo fired from the North Korean submarine.

They are the latest in a recent series of cyber attacks and incidents in the two countries.

North Korea’s Internet connection was severely disrupted for almost two days from March 13 to March 15. The country’s state-run news agency, KCNA, accused the U.S. and its allies of launching an attack, but little evidence was provided or has been found to determine exactly what happened.

Then last week an estimated 26,000 PCs at three major South Korean TV broadcasters and three banks were hit by malicious software that wiped their hard disk drives. South Korean investigators are still looking into the attacks and have yet to determine their source.