Iranian oil shipments advanced 13 % last month even as the U.S. implemented new sanctions against the Gulf country, according to the International Energy Agency(IEA).Imports from Iran rose to 1.28 million barrels a day in February from 1.13 million barrels in January, the Paris-based adviser to 28 oil-consuming nations said in a report Wednesday. U.S. rules took effect last month that require importers to pay in local currencies kept in escrow accounts, the agency said.The U.S. and allies are restricting Iran’s oil exports to pressure the government in Tehran to stop enriching uranium. Negotiators will meet in Kazakhstan next month to discuss steps toward an agreement on Iran’s nuclear program.“The only thing clear is that the current stalemate between Iran and the West is unsustainable,” the IEA said in the report. “Sooner or later, something has to give.”Iran bought secondhand tankers to take oil to China, the IEA said, citing industry reports. The country is also ordering vessels to turn off transponders signaling ships’ locations, destinations and depths in the water, complicating the compilation of exports data, according to the Iranian Mehr news agency Thursday.The shipments estimates are based on import data submitted by nations in the Organization for Economic Cooperation and Development, information from customs agencies, and news reports for individual countries, the IEA said. Tanker-tracking is the only source of information for the most current month, according to the report.Exports will average 1.38 million barrels a day in the Iranian fiscal year starting March 21, 2013, the IEA estimates.That’s in line with the government’s budget expecting 1.3 million barrels a day, according to the report. Oil sales once accounted for half of government revenue, according to the U.S. Department of Energy.