The assessment by Gen. Nikolai Makarov, chief of Russia's General Staff, came as world leaders ramp up pressure on Tehran over its nuclear aspirations and threaten another round of sanctions, the Russian news agency RIA Novosti reported. U.S. officials said it wouldn't rule out any options.
Iran last week announced it has enriched its first batch of uranium to 20 percent and said it would consider a compromise on enriching uranium for medical purposes only if changes it offered to the compromise were adopted.
"The consequences, I believe, would be dreadful for Iran, as well as Russia, the entire Asia-Pacific community," if force were used against Iran, Makarov said.
Russia, which has strong business ties with Iran and has been reluctant to endorse new sanctions, recently joined calls for Iran to curbing its nuclear program, which Western leaders said they fear is for weapons production. Iran maintains its program is for peaceful purposes.
During his visit to Russia, Israeli Prime Minister Benjamin Netanyahu said he didn't believe the sanctions under consideration by the U.N. Security Council would be effective, RIA Novosti said. Netanyahu met with Russian leaders to try to persuade them to support tough additional sanctions against Iran.
"It is necessary to exert pressure on Iran to try to prevent it from creating nuclear weapons because the obtaining of nuclear weapons by Iran will have a negative effect on the world and the (Middle East) region," Netanyahu told Russian business daily Kommersant.
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