US stocks declined on Thursday as investors became more cautious in the wake of attacks in Afghanistan and upcoming statements from the Federal Reserve, which may provide more clues about its approach to reducing stimulus.

To be more specific, the S&P 500 fell 0.45% after reports came that there were casualties in the attack outside Kabul airport. Non-voting FOMC members also made hawkish comments on monetary policy, urging the Fed to begin narrowing its asset-buying program.

Energy stocks spearheaded the fall amid decline in oil prices.

Michael O'Rourke, chief market strategist at Jonestrading, said the plunge is most likely caused by the recent news, including uncertainty sparked by the Fed comments ahead of Chairman Jerome Powell's speech at the Jackson Hole symposium. Opinions were divided as to whether the statements would provide clearer guidance on cutting urgent support from the Fed.

But while continued economic recovery and heightened inflation add to the argument for starting policy normalization, the rapidly spreading delta strain threatens a slower recovery than some expected.

Christopher Murphy, co-head of derivatives strategy at Susquehanna International Group said: "While news of bombings at the Kabul airport has resulted in some volatility this morning, it has become consensus that Jackson Hole will be more or less a non-event as investors are moving expectations for any major Fed taper announcement to later this year."

And if Powell does not give a hint on when the cut will be announced, Independent Advisor Alliance CIO Chris Zaccarelli said investors will focus on the August employment report.

"A strong jobs report on Sept. 3 will lead to increased speculation that the Fed will announce their taper plans at the September FOMC meeting," noted Zaccarelli. "However, any weakness or disappointment in that report will push consensus back to the next Fed meeting," he added.

Other important events for this week are:

- Jackson Hole symposium (from Thursday to Saturday);

- report on US income and expenses;

- data on PCE price index;

- speech of Fed Chairman Jerome Powell.