World War 3 fears are on the rise after Russia sent a sharp warning to the United States over involvement in Syria.

The United States had been conducting strategic air strikes against ISIS in both Iraq and Syria, but announced this week that for the first time there would be on-the-ground troops fighting the militant group. U.S officials said it would be a group of “fewer than 50” troops who would train and assist opposition forces, the first time the United States would openly operate in Syria.

This comes just weeks after Russia started a series of air strikes in Syria, and led Russian Foreign Minister Sergei Lavrov to issue a warning to the United States about sparking a proxy war.

“I am convinced that neither the United States nor Russia of course want any kind of slide into a so-called proxy war,” he said (via the BBC). “But to me it is obvious that this situation makes the task of co-operation between the militaries even more relevant.”

This is not the first time that fears of World War 3 have cropped up over the tension in Syria. When Russia last month started a series of air strikes in Syria, many believed that Putin was not trying to stamp out ISIS but instead was striking out against rebels trying to topple leader Bashar Assad.

Some witnesses even noted that the strikes did not take place anywhere near the ISIS strongholds in Syria.

The United States has also been fighting against ISIS in Syria, but has aligned with rebel groups that oppose Assad. There were reports that the first round of air strikes conducted by Russia did not hit ISIS at all, but instead these U.S.-backed rebels.

In this week’s announcement, White House spokesman Josh Earnest said that President Obama wants to give greater support to rebels that have been pushing back against ISIS.

“There are now moderate opposition forces that are 45 miles outside [IS stronghold] Raqqa,” he said. “The president is prepared to intensify the elements that have shown promise.”

“This is an intensification of a strategy he discussed a year ago.”

The fears of World War 3 have also crept into American politics, with GOP frontrunner Donald Trump warning against other candidates he believes would get the United States bogged down into a proxy war with Russia.

“They want to start World War III over Syria. Give me a break,” Trump said at the State Fairgrounds in Oklahoma City (via the Hill).

“You know Russia wants to get ISIS right. We want to get ISIS. Russia’s in Syria. Maybe we should let them do it?” he continued. “Let them do it. What the hell are we crazy?”

This stance could have a bigger effect if Trump were to win the GOP nomination. He has been a harsh critic of the war in Iraq, and doesn’t appear too willing to bring the United States into another large conflict.

“I said don’t go into Iraq. I’m the most militant person here, the most militaristic person you’ll ever meet. I believe in the military strongly but I didn’t want to see us invade Iraq,” he said. “We spend $2 trillion dollars, thousands of lives, wounded warriors all over the place that I love by the way… we got nothing. We can’t even go over there.”

The fears extend beyond American politics. There are theories that Vladimir Putin may be trying to spark World War 3 in Syria to distract from the growing domestic problems within Russia, which The Rand Daily Mail said would be a “useful distraction” for the Kremlin.

[Picture by Chip Somodevilla/Getty Images]