By Suzanne McGee, Saqib Iqbal Ahmed and Lewis Krauskopf

NEW YORK (Reuters) -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.

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.  

"I think the markets are going to be initially alarmed, and I think oil will open higher," said Mark Spindel, chief investment officer at Potomac River Capital.

"We don't have any damage assessment and that will take some time. Even though he has described this as 'done', we're engaged. What comes next?" Spindel said. 

"I think the uncertainty is going to blanket the markets, as now Americans everywhere are going to be exposed. It's going to raise uncertainty and volatility, particularly in oil," he added.

Spindel, however, said there was time to digest the news before markets open and said he was making arrangements to talk to other market participants. 

OIL PRICES, INFLATION

A key concern for markets would center around the potential impact of the developments in the Middle East on oil prices and thus on inflation. A rise in inflation could dampen consumer confidence and lessen the chance of near-term interest rate cuts.  

"This adds a complicated new layer of risk that we'll have to consider and pay attention to," said Jack Ablin, chief investment officer of Cresset Capital. "This is definitely going to have an impact on energy prices and potentially on inflation as well."

While global benchmark Brent crude futures have risen as much as 18% since June 10, hitting a near five-month high of $79.04 on Thursday, the S&P 500 has been little changed, following an initial drop when Israel launched its attacks on Iran on June 13.

Before the U.S. attack on Saturday, analysts at Oxford Economics modeled three scenarios, including a de-escalation of the conflict, a complete shutdown in Iranian oil production and a closure of the Strait of Hormuz, "each with increasingly large impacts on global oil prices." 

In the most severe case, global oil prices jump to around $130 per barrel, driving U.S. inflation near 6% by the end of this year, Oxford said in the note.   

"Although the price shock inevitably dampens consumer spending because of the hit to real incomes, the scale of the rise in inflation and concerns about the potential for second-round inflation effects likely ruin any chance of rate cuts in the U.S. this year," Oxford said in the note, which was published before the U.S. strikes.    

In comments after the announcement on Saturday, Jamie Cox, managing partner at Harris Financial Group, agreed oil prices would likely spike on the initial news. But Cox said he expected prices to likely level in a few days as the attacks could lead Iran to seek a peace deal with Israel and the United States.  

"With this demonstration of force and total annihilation of its nuclear capabilities, they’ve lost all of their leverage and will likely hit the escape button to a peace deal," Cox said.

Economists warn that a dramatic rise in oil prices could damage a global economy already strained by Trump's tariffs.

Still, any pullback in equities might be fleeting, history suggests. During past prominent instances of Middle East tensions coming to a boil, including the 2003 Iraq invasion and the 2019 attacks on Saudi oil facilities, stocks initially languished but soon recovered to trade higher in the months ahead.

On average, the S&P 500 slipped 0.3% in the three weeks following the start of conflict, but was 2.3% higher on average two months following the conflict, according to data from Wedbush Securities and CapIQ Pro.

DOLLAR WOES

An escalation in the conflict could have mixed implications for the U.S. dollar, which has tumbled this year amid worries over diminished U.S. exceptionalism.

In the event of U.S. direct engagement in the Iran-Israel war, the dollar could initially benefit from a safety bid, analysts said.

"Do we see a flight to safety? That would signal yields going lower and the dollar getting stronger," said Steve Sosnick, chief market strategist at IBKR in Greenwich, Connecticut. "It’s hard to imagine stocks not reacting negatively and the question is how much. It will depend on Iranian reaction and whether oil prices spike." 

(Reporting by Saqib Iqbal Ahmed, Lewis Krauskopf, Suzanne McGee and Saeed Azhar; Editing by Megan Davies, Diane Craft, Peter Henderson, Marguerita Choy and Jamie Freed)