Oil prices on Tuesday climbed to their highest since 2014 as Yemeni popular forces attacked the United Arab Emirates, warning it could target more facilities.

Iran PressEurope: International benchmark Brent crude futures advanced 1.19% to $87.51 per barrel, while US West Texas Intermediate futures settled 2.43% higher at $85.43 per barrel. Both oil contracts notched their highest level since October 2014 earlier in the day after a subdued trading day on Monday as U.S. markets were closed for a public holiday.

Energy analysts have attributed oil’s bullish run over recent weeks to signs of tightness in the market and persistent worries of a Russian incursion into Ukraine. The rising threat of a further deterioration in the Middle East’s security climate has provided further support to oil prices, prompting some to forecast a return to triple digits.

Yemeni popular forces claimed responsibility for the attack, which took place Monday morning and caused huge fires that resulted in three petroleum tanker explosions near state oil firm ADNOC’s storage facilities. The fires began in the industrial area of Musaffah and at a construction site near Abu Dhabi International Airport in the UAE capital, Abu Dhabi police said in a statement, adding that they believe the attack was carried out by drones.

The UAE is the third-largest oil-producing member of OPEC, and ADNOC — the Abu Dhabi National Oil Company — controls oil operations in Abu Dhabi, home to the vast majority of the state’s crude. The UAE is the world’s seventh-biggest oil producer, pumping just over 4 million barrels per day.