Syrian President Bashar Assad has the upper hand in Syria now that Russia has stepped up its military campaign in the country and Iran has sent more pro-regime troops to fight, Pentagon officials said Tuesday.

"The balances of forces are now in Assad's advantage," Gen. Joe Dunford, chairman of the Joint Chiefs of Staff, said in an Armed Services Committee hearing Tuesday morning.

Dunford and Secretary of Defense Ash Carter said in the hearing that although Assad has in the past month gained a significant military advantage in Syria, the U.S. has a priority of defeating the Islamic State group, not the regime.

Assad has overseen the killing of hundreds of thousands of people since 2011 when the revolution began and for more than four years the U.S. has maintained the position that there is no future for Syria as long as he is president. But following the Russian military intervention in Syria last month, the rhetoric within the administration changed. Officials no longer denounced Assad as a dictator or tyrant. Instead, both Secretary of State John Kerry and President Obama said the U.S. is willing to work with Assad’s allies, including Iran and Russia, to find a way to end the conflict.

So far the U.S. has held meetings, at least publicly, only with Russian officials, including Foreign Minister Sergey Levrov. That interaction has angered rebels inside Syria that are being armed by the U.S. but bombed by Russia. Last week, rebels in Aleppo told International Business Times in a series of interviews that Russia was deliberately targeting them, especially in the countryside, and the Islamic State group was gaining ground as a result. The introduction of Iran into the diplomatic mix would only escalate those tensions and could also anger U.S. allies in the Persian Gulf.

On Tuesday, regime forces gained ground in the Aleppo countryside, where rebels armed by the U.S. are battling Assad and ISIS. Russian forces also hit several targets in Hama, a city just south of Aleppo where the United Nations said this week thousands of people have been displaced.