A U.S. attack on Iranian nuclear sites on Saturday could lead to a knee-jerk reaction in global markets when they reopen, sending oil prices higher and triggering a rush to safety, investors said, as they assessed how the latest escalation of tensions would ripple through the global economy, Reuters reported.

The attack, which was announced by President Donald Trump on social media site Truth Social, deepens U.S. involvement in the Middle East conflict. That was the question going into the weekend, when investors were mulling a host of different market scenarios.

In the immediate aftermath of the announcement, they expected the U.S. involvement was likely to cause a selloff in equities and a possible bid for the dollar and other safe-haven assets when trading begins, but also said much uncertainty about the course of the conflict remained.

While Trump called the attack "successful", few details were known. He was expected to address the nation later on Saturday, according to Reuters.