Brent crude futures fell 45 cents, or 0.65%, to $68.66 a barrel. US West Texas Intermediate crude declined 44 cents, or 0.66%, to $67.01 a barrel.

Both contracts rose to their highest in one week on Wednesday as Iran suspended cooperation with the United Nations nuclear watchdog.

Raising concerns the lingering dispute over the Middle East producer's nuclear program may again devolve into armed conflict, and the US and Vietnam reached a preliminary trade deal.

Still, there is increasing uncertainty around US trade policy as the 90 day pause on the implementation of higher tariffs will end on July 9 without any new trade deals with several large trading partners such as the European Union and Japan.

Additionally, the Organisation of the Petroleum Exporting Countries (OPEC) and its allies such as Russia, known as OPEC+ will likely agreed to raise their output by 411 000 barrels per day (bpd) at their meeting this weekend.

With the uncertainty around both events, and the upcoming July Fourth Independence Day holiday in the US, "market participants will probably not want to carry too much risk into the long US weekend," ING analysts said in a note on Thursday.

Adding to the negative sentiment, a private-sector survey showed on Thursday service activity in China, the world's biggest oil importer, expanded at the slowest pace in nine months in June as demand weakened and new export orders declined.

A surprise build in US crude inventories also highlighted demand concerns in the world's biggest crude consumer.

--Reuters--