Oil prices fell on Wednesday, with U.S. futures dipping below $70 a barrel for the first time in a month, after U.S. stockpiles rose by 6.5 million barrels, almost triple what analysts had forecast, while exports dropped.

U.S. light crude oil CLc1 slumped $1.84, or 2.6 percent, to $70.08 a barrel by 12:19 p.m. EDT (16:19 GMT), after falling as low as $69.63, Reuters reported.

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Oil had been rising on worries about Iranian sanctions and tensions between the United States and Saudi Arabia after the death of Saudi journalist Jamal Khashoggi.

"This market is dangerously close to $70. If it goes down through $70, I think some of that speculative position may have interest in getting out, and that could accentuate the downside," said Bob Yawger, director of futures at Mizuho in New York.

Brent crude LCOc1 was down $1.38, or 1.7 percent, at $80.02 a barrel, after gaining $1.15 over the previous three sessions. The global benchmark is trading nearly $7 below a four-year high of $86.74 reached on October 3.

U.S. crude stocks rose 6.5 million barrels last week, the fourth straight weekly build, as exports were down to 1.8 million barrels per day, the U.S. Energy Information Administration said, in a report analysts characterized as bearish.