Brent crude futures were down $1.10, or 1.4 percent, at $77.76 a barrel by 0112 GMT. US crude was down 68 cents, or 0.9 percent, at $73.43.
Both contracts had posted gains earlier in the previous session after industry data showed inventories fell more than expected last week in the United States.
Washington will consider requests from some countries to be exempted from sanctions it will put into effect in November to prevent Iran from exporting oil, US Secretary of State Mike Pompeo said on Tuesday.
"There will be a handful of countries that come to the United States and ask for relief from that. We'll consider it," Pompeo said, according to the text of an interview in Abu Dhabi with Sky News Arabia released by the US State Department. He did not identify any countries.
Washington had earlier told countries they must halt all imports of Iranian oil from Nov. 4 or face US financial measures, with no exemptions.
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