Johnson & Johnson says it is delaying the rollout of its coronavirus vaccine in Europe amid a U.S. probe into rare blood clots.

The company announced the decision Tuesday after regulators in the United States said they were recommending a “pause” in administration of the single-dose shot to investigate reports of potentially dangerous blood clots.

“We have been reviewing these cases with European health authorities,” the company said. “We have made the decision to proactively delay the rollout of our vaccine in Europe.”

Hundreds of thousands of doses of the vaccine were due to be shipped to Europe in the coming weeks.