Russia's Foreign Ministry denounced the tightening of U.S. unilateral sanctions against Iran as "unacceptable and contradictory to international law," Interfax news agency reported Tuesday.

"Such a practice seriously complicates the constructive dialogue with Tehran," spokeswoman Maria Zakharova said.

The new sanctions, in line with the interests of some countries, would not promote negotiations with Iran, she said.

According to the ministry, the sanctions would affect companies from a third country cooperating with Iran in the oil and refining industry and banking sector.

Tougher sanctions against Tehran were no longer in accordance with the nuclear nonproliferation objectives, it said.

The new U.S. moves came in response to a report released by the International Atomic Energy Agency, which outlined alleged activities pointing to clandestine nuclear bombs making by Iran.

Tehran has denied Western countries' charges that it is seeking nuclear arms, stressing instead the peaceful purpose of its nuclear program.