Russian Foreign Minister Sergei Lavrov said on Saturday a recently announced guideline on the operation of US nuclear assets on the Korean peninsula is certain to add security concerns in the region.
South Korean and Russian news agencies reported.
Speaking at a meeting of the Association of Southeast Asian Nations in Laos, Lavrov said he had not been briefed on the details of the plan but that it concerns Russia, Yonhap agency reported.
"Another element of concern is that the United States recently concluded an agreement with the Republic of Korea on joint nuclear planning," Lavrov was quoted as saying by the Russian state-run RIA news agency.
"So far, we can't even get an explanation of what this means, but there is no doubt that it causes additional anxiety."
The guideline is aimed at responding to the nuclear threat from North Korea, the U.S. and South Korea have said.

South Korean ferry runs aground, all 267 people rescued
Indonesia's Semeru volcano erupts, alert level raised to highest
19 killed and 66 wounded in heavy Russian attack on Ukraine
Elon Musk, Ronaldo attend Trump's dinner for Saudi Crown Prince
Louvre museum to add 100 external cameras by 2026 after heist