Russia's national currency, the ruble, weakened significantly at the beginning of Thursday's regular trading session, having reached its minimum rate over two years, due to the threat of new sanctions U.S. being imposed against Russia and further tightening of the American sanctions policy.

The dollar exchange rate has reached RUB 66.73 for the first time since early August 2016, while that of the euro has been set at RUB 77.33 for the first time from April this year, according to Reuters.

Since the beginning of the week, the Russian ruble has dropped against the U.S. dollar by almost 4.4%.

Washington on Wednesday evening said it would impose new sanctions on Russia by the end of August, having ensured that Moscow used a nerve agent to poison ex-Russian double agent Skripal and his daughter Yulia in the UK.

Sanctions will affect products that are significant to Russia's national security, a senior State Department spokesman told reporters at a press conference referring to Chemical and Biological Weapons Control and Warfare Elimination Act of 1991. He also noted the possibility of further restrictions.

On Wednesday morning, the Russian daily Kommersant published new proposals by U.S. lawmakers on prohibitive measures against Russia, including the blocking of dollar payments to Russian banks and ban on transactions with the new Russian national debt for U.S. residents.