S&P 500 futures and oil futures flashed an unusual burst of activity early Monday minutes before a market-moving social media post from President Donald Trump.

At around 6:50 a.m. in New York, S&P 500 e-Mini futures trading on the CME recorded a sharp and isolated jump in volume, breaking from an otherwise subdued premarket backdrop. With thin liquidity typical of early trading hours, the sudden burst stood out as one of the largest volume moments of the session up to that point.

A similar pattern was observed in oil markets. West Texas Intermediate May futures also saw a noticeable pickup in trading activity at roughly the same time, with a distinct volume spike interrupting otherwise quiet conditions.

Roughly 15 minutes later, at 7:05 a.m., Trump said on Truth Social that the U.S. and Iran had held talks and that he was halting planned strikes on Iranian power plants and energy infrastructure. That announcement prompted an instant rally in risk assets, with S&P 500 futures soaring more than 2.5% before the opening bell. West Texas Intermediate futures dropped nearly 6% following the announcement.

The timing of the earlier volume spikes across both equities and crude caught the attention of traders, particularly given the absence of an obvious catalyst at the moment they occurred.

Early-morning futures markets are typically less liquid, which can make short bursts of buying and selling more noticeable than during regular trading hours. Still, the trades raised some eyebrows because whoever purchased a large amount of stock futures and sold or short crude futures at that moment made a lot of money just minutes later.

The U.S. Securities and Exchange Commission and the CME Group didn’t immediately respond to CNBC’s requests for comment.

To be sure, algorithmic and macro-driven strategies can also generate rapid flows across asset classes without a single identifiable catalyst in early trading.

— With assistance from CNBC’s Fred Imbert.