China is overtaking the U.S. as a buyer of Middle East oil, adding fuel to diplomatic tension between the nations over security in the region.

China surpassed the U.S. as importer of Persian Gulf crude several years ago, by some measures. Now it is on track to overtake the U.S. this year as the world's No. 1 buyer of oil from the Organization of the Petroleum Exporting Countries, the largely Middle Eastern energy-exporting bloc.

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