As the United States and allies consider taking military action against the Syrian regime over the alleged use of chemical weapons, the price of oil rose and markets dropped on Tuesday over fears of increased instability in the region.

The price of oil closed at $109 a barrel on Monday, the highest price in 18 months. Traders are concerned that an intensified Syrian conflict could involve Iran, a major oil producer and ally to the Syrian regime. While Syria is not a major oil producer, it shares an eastern border with Iraq, another major oil producer.

ALSO READ: U.N. Chemical Weapons Team Attacked By Snipers In Syria

The price of oil was also affected by protests in Libya, which shut down production in its western oil fields.

Benchmark stock indexes were also down on Tuesday.  The Dow Jones industrial average was down 115.93 points during midday trading.  The S&P 500 also dropped nearly one percent.

According to the Los Angeles Times, the markets were reacting to news that the U.S. is considering a military strike on Syria as early as Thursday.

Read more about the Syrian conflict at the Washington Post.

Reach Executive Producer Colin Hale here. Follow him on Twitter.