SEOUL (Reuters) - Russian President Vladimir Putin said he plans to lift relations with North Korea to a higher level and pledged his unwavering support, Pyongyang's state media KCNA reported on Tuesday ahead of his planned visit to the country.

In a letter published in North Korea's Rodong Sinmun, a ruling Workers' Party mouthpiece, Putin said the two countries have developed good relations and partnerships over the past 70 years based on equality, mutual respect and trust.

Putin thanked North Korea for supporting what Russia calls its special military operation in Ukraine, and vowed support for Pyongyang's efforts to defend its interests despite what he called "U.S. pressure, blackmail and military threats."

The article was published a day after the two countries announced that Putin will visit North Korea for the first time in 24 years for two days starting on Tuesday.

(Reporting by Hyonhee Shin and Josh Smith, Editing by Rosalba O'Brien)