Russian Foreign Minister Sergei Lavrov said in a statement: "We are concerned about the situation surrounding Syria. It is important not to provoke further tension in a region already overflowing with crises.
"If there are some remaining concerns, they should be backed up by concrete proof and resolved through negotiations. The language of threats can only worsen the situation."
Syrian President Bashar al-Asad arrived on Monday for a four-day official visit to Russia and was to hold talks on Tuesday with his Russian counterpart Vladimir Putin over strengthening bilateral relations.
The visit comes as Washington continues to accuse Syria of sponsoring what it calls "international terrorism" and turning a blind eye to anti-US fighters crossing the border into neighbouring Iraq.
US President George Bush warned Syria last month against "meddling" in Iraq and said Washington had a variety of diplomatic and economic measures it could take.
Al-Asad's talks in Moscow have been marred by controversy because Israel says Russia is planning to sell advanced missiles to Syria, allegations dismissed by Moscow.