Futures tracking Wall Street’s main indexes fell this morning in the last session of a holiday-truncated week after President Donald Trump signaled more aggressive attacks on Iran, dampening expectations for a swift end to the Middle East conflict.

After Trump floated the possibility of strikes on Iranian energy infrastructure, oil prices surged about 7%, taking Brent crude futures to $108 per barrel. Energy stocks in the U.S. climbed, with Exxon Mobil and Chevron up 3.1% and 2.6%, respectively, in premarket trading.

“Uncertainty is kryptonite for markets and between the contradictory messages from Trump, disputed claims on both sides, and the lack of clarity on a plan that can provide a resolution to the conflict, they are getting a heavy dose of it,” said Russ Mould, investment director at AJ Bell.

Still, Wall Street’s three indexes looked set to post their biggest weekly rise in four months. This would be their first week of gains in six. Earlier this week, markets were optimistic that an end to the war was near.