Russian warplanes initiated a series of airstrikes over Syria on Wednesday, adding an additional reason for the United States to feel concern over the situation in the Middle East. According to a report from the Washington Post, Russia’s involvement significantly complicates the multi-year war that has cost the world billions of dollars and created millions of refugees.

Washington was quick to criticize the airstrikes, which they claim fell upon targets where members of the Islamic State were likely not even present. U.S. officials claimed that Moscow’s involvement would not take precedent over an American-led campaign targeting IS fortifications by air in Syria.

The Russian airstrikes also highlight Putin’s interest in the Middle East, particularly in Syria. Putin expressed to the U.N. this week his opinion that Syria’s government, led by president Bashar Al-Assad was crucial to maintaining stability in the country. President Obama argued that considering the atrocities Assad has carried out against his own people, including bombing sovereign towns and villages, could not continue any longer.

Russian planes struck just hours after Moscow authorized the use of military force against the Islamic State. U.S. Secretary of State John Kerry doubled down on President Obama’s argument, stating that military alliance with Assad’s government is not the answer to the tumult occurring in the region.

A bona fide alliance between the Russians and Assad’s government would mean trouble for efforts to stabilize embattled regions in the Middle East. U.S. policy follows a desire to keep conflict at a minimum, where Russians may begin standing by the Syrian government against anyone it perceives as hostile.

According to one of Putin’s spokesmen, Dmitry Peskov, “Russia will factually be the only country to carry out this operation on the basis of the request of the legitimate government of Syria.”

It remains to be seen how Russia’s involvement in the conflict will influence outcomes in Syria and beyond, but for now U.S. officials are understandably on edge.