The Russian ruble briefly weakened to worse than 70 to the U.S. dollar for the first time since March 2016, bringing its losses this year to 19 percent.

Amid concerns about the economy and uncertainty about U.S. sanctions, the Russian currency hit 70.16 when trading opened on September 10.

It later strengthened, dipping below 70 again.

Factors putting pressure on the ruble include U.S. sanctions and the possibility of more punitive measures as well as a sell-off of other emerging-market countries.

Reuters reported that ruble's fall is likely to be limited by Russian export-focused companies that often sell foreign currency when it is strong, buying rubles they need for domestic obligations such as tax payments that are due in the second half of the month.

The United States and European Union have imposed a series of sanctions on Russia since 2014 in response to actions including the seizure of Crimea and support for armed separatists in eastern Ukraine.

On August 8, the U.S. State Department announced new sanctions aimed at punishing Moscow for the poisoning of former Russian spy Sergei Skripal and his daughter in England in March with a rare nerve agent known as Novichok.

The initial tranche of those sanctions took effect in late August. A second tranche would kick in if Russia misses a November deadline to fulfill conditions such as providing "reliable assurances" that it will no longer use chemical weapons.

Based on reporting by Reuters, Bloomberg, and TASS