(Bloomberg) -- The Taliban has seized key customs posts and is collecting import duties on goods entering Afghanistan, a Ministry of Finance official said, cutting off a key revenue source for President Ashraf Ghani’s beleaguered government.

The ministry collected only 4.6 billion Afghanis ($58 million) in duties last month compared with 7.3 billion Afghanis in June from all 30 customs posts located on borders, cities and airports, ministry spokesman Mohammad Rafi Tabe said by phone. Most losses were at international border crossings where the Taliban took more than 2.7 billion Afghanis, he said.

The militant group has been making rapid advances across the country as U.S. and NATO troops head home, with a final exit slated for Aug. 31. Over the last month they have gained control of at least eight of 14 customs posts along Afghanistan’s borders with Iran, Pakistan, Turkmenistan and Tajikistan, Tabe said.

Import duties account for about half of Afghanistan’s total domestic revenues, which were estimated at about 216.5 billion Afghanis this year, Tabe said. The U.S. and other international donors also provide around 236 billion Afghanis annually to help the aid-dependent country finance its military expenses.

Afghan Defense Ministry spokesman Fawad Aman vowed the government would retake the customs posts by using “full force” against the Taliban on the ground and in the air. A Pentagon watchdog warned last month the country would suffer serious financial losses if the customs posts stayed out of government control.

“The Taliban’s occupation of key border crossings could deny potentially significant levels of customs revenue to the Afghan government, further inhibiting its ability to generate sufficient domestic revenues,” the Special Inspector General for Afghanistan Reconstruction, said in a July 30 report.

Taliban spokesman Zabihullah Mujahed confirmed control of the customs posts, adding that the group has reduced most duties by as much as 40% to boost trade. Afghanistan mostly imports food items, construction material and fuel, according to Tabe.

The militant group has dramatically expanded their hold on Afghan territory in recent months -- controlling half of the country’s 419 districts -- and is now putting military pressure on the provincial capitals, General Mark Milley, chairman of the Joint Chiefs of Staff, said on July 22. Afghan security forces are consolidating around Kabul and provincial capitals as Taliban fighters attempt to isolate those population centers, he added.

Tabe said the seized border posts include Islam Qala, Torghundi and Abu Nasr Farahi in the west; Spin Boldak in the south; Dand-e-Patan in the east; and Sher Khan Bandar, Ay Khanum and Ishkashim in the north and northeast.

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