The United States warned Americans in Mali on Tuesday to leave the country immediately using commercial flights, as its government comes under increasing pressure from al Qaeda-linked insurgents, who are imposing a fuel blockade.

Jama’at Nusrat al-Islam wal-Muslimin militants announced a blockade on fuel imports to the landlocked West African country in early September. They have since attacked convoys of fuel tankers attempting to enter the country or reach the capital, Bamako.

The government on Sunday ordered the suspension of school and university classes throughout Mali for two weeks due to the fuel shortage.

“Persistent infrastructure challenges in Mali including continued disruptions of gasoline and diesel supplies, the closure of public institutions such as schools and universities nationwide, and ongoing armed conflict between Malian government and terrorist elements around Bamako increase the unpredictability of Bamako’s security situation,” the U.S. embassy in Mali said in a statement.

Analysts have described the fuel blockade as part of a pressure campaign on Mali’s military-led government by militant groups, who want to cut off the country’s economic oxygen.

The airport in Bamako remains open, the embassy said, advising Americans to depart using commercial flights rather than traveling over land to neighboring countries due to the risk of “terrorist attacks along national highways.”

U.S. citizens who choose to remain in Mali should prepare contingency plans, including for sheltering in place for an extended period, it said.

The embassy is not able to provide support to Americans outside the capital.

On Friday, the State Department authorized the departure of non-emergency U.S. government personnel and family members from Mali due to safety risks.

The travel advisory level for Mali is level 4, or “do not travel”.

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(Reporting by Daphne Psaledakis in Washington and Portia Crowe in Dakar; Editing by Joe Bavier)