Oil prices reached 100 dollars a barrel for the first time since May after attacks by Iranian backed Houthi militants in the Red Sea raised fears of tighter global supplies and a renewed inflation shock.

Brent crude, Nigeria’s benchmark, rose more than 6 percent to 100 dollars, extending a sharp rebound this month amid concerns that the United States and Iran are heading toward renewed full scale conflict. The rally accelerated after the Houthis said they had attacked two Saudi Arabian tankers in the Red Sea following their move to impose a naval blockade on the kingdom earlier in the week, raising fears they could move to close the Bab al Mandab Strait, a critical route for Saudi oil exports since Iran took control of the Strait of Hormuz early in the conflict.

Brent had last traded at 100 dollars in late May before falling back in June after Washington and Tehran agreed to extend a ceasefire and reopen the strait. The latest escalation follows the breakdown of that ceasefire, with US and Iranian forces exchanging fire for almost two weeks. President Donald Trump warned the Houthis and Iran on Thursday that they would face major military consequences if the attacks continue, while US Secretary of State Marco Rubio said this week that Iran’s leadership appears unwilling to negotiate.

The renewed conflict risks pushing up inflation in many countries, including Nigeria, as higher oil prices typically raise the cost of petrol and diesel, with businesses passing higher transport costs on to consumers through the price of goods including food.