According to U.S. military commanders, American and Russian troops are fighting within "hand-grenade range" of each other in certain areas of Syria in the ongoing fight to combat ISIS, even though they are supporting opposite sides in the still ongoing Syrian Civil War. Troops from both countries are so close to each other due to the fact that both sides are backing the Kurdish People's Protection Units (YPG) fighters.

Why are both sides backing the YPG?

The United States and Russia are both supporting the Kurdish YPG fighters because they are one of the major groups on the ground that is taking the fight to ISIS in Syria and Iraq.

The Pentagon halted military-to-military cooperation with Russia since their annexation of Crimea back in 2014. However, commanders on both sides are now in contact as a result of the close fighting. This strange cooperation between both sides is in the short-term interests they both have in defeating ISIS, especially with it being touted as a major priority of President Trump's administration.

Potential for collateral damage?

The Kurdish YPG fighters that the Americans and Russians are supporting do not take any orders from either side and run their own military operations. The United States and Russia only coordinate with the YPG to give them artillery and air support during their battles against ISIS.

It is unknown how many American or Russian troops are on the ground in Syria, but estimates range from under 1,000 on the American side and between 1,600 and 4,500 on the Russian side. Due to their close proximity, troops on the ground, and that fact that neither side is giving out orders to the YPG, there is potential for collateral damage, which could further escalate matters between the U.S.

and Russia.

How will Turkey respond?

During the first two weeks of March both America and Russia worked with the Kurdish YPG to prevent the Turkish army from entering the town of Manbij in northern Syria. By working with the YPG Russia is risking their recent understanding with Turkey after recent escalation. The U.S. is risking infuriating their important ally and NATO member by working with the YPG. This is because Turkey considers the YPG to be terrorists and worries that they might work with the Kurds in Turkey to try to create their own state.