MEXICO CITY – A Mexican border city has begun fining U.S. drivers who cross the border to fill extra drums, tanks or barrels with government-subsidized Mexican fuel.

The city of Ciudad Acuna, across the border from Del Rio, Texas, said Friday that it fined four U.S. residents for carrying extra diesel and would impound their cars until they pay. The fines equal 70 percent of the value of the diesel confiscated.

U.S. drivers can fill up their own vehicles, but carrying extra fuel containers back across the border violates customs regulations and possibly safety rules, a report from the city said.

Mexico, one of the world's top 10 oil producers, sells diesel fuel domestically at subsidized prices of about US$2.25 per gallon, about half the U.S. price.

Mexican filling stations near the U.S. border have seen an increase in American drivers who cross over to fill up. Mexican truckers and drivers complain the run on fuel is causing temporary shortages and longer lines for them.