South Korea expressed strong regret Thursday over the remarks by Russia's top envoy to North Korea that the likelihood of another nuclear test by Pyongyang will depend on how far Seoul and Washington will go in taking their deterrence measures against the North.

Russian Ambassador to North Korea Alexander Matsegora said in an interview with the TASS news agency the previous day that North Korea may decide to conduct its seventh nuclear test if Washington continues to take "provocative steps" on and around the Korean Peninsula.

Matsegora almost derided the United States and its allies for "speculating" about whether and when the North will carry out another nuclear test, saying his host country will likely do so for its own defense if Washington keeps "flying strategic bombers over the peninsula."

"We think it's very regrettable that the Russian ambassador to North Korea made comments that shift the blame on South Korea and the United States for North Korea's provocations and justify the North's nuclear development," foreign ministry spokesperson Lim Soo-suk said in a briefing.

Lim said firming up the security posture is a natural measure to protect the lives of the South Korean people and ensure their safety.

"The need for the trilateral security cooperation among South Korea, the U.S. and Japan will increase as the military threats from Russia and North Korea continue," Lim added.