“If we don't get a breakthrough in Moscow there is no question we will continue to ratchet up the pressure," David Cohen, U.S. Treasury undersecretary for terrorism and financial intelligence, said in an interview with The Haaretz daily.

Russia is hosting the third round of talks on Iran’s nuclear program June 18-19.

Cohen said sanctions on Iran are biting, but more will be done to pressure the Islamic Republic to abandon its nuclear program.

"The sanctions are having an impact on Iran, but I also recognize that more needs to be done. And we are intent on doing more," he said.

The previous four rounds of Iran Six talks were held in Baghdad on May 23-24.

Western nations and Israel are seeking to persuade Iran to give up its uranium enrichment program, which they suspect is aimed at producing nuclear weapons. Iran says its nuclear program is merely designed to generate energy.

The Iran Six have presented proposals on how to resolve concerns over Iran’s current 20% uranium enrichment. Iran has expressed readiness to discuss this and other issues, including what it calls its right to pursue nuclear research.