Morgan Stanley downgraded global equities and upgraded cash and US government bonds, as investors shun risk in favour of safe-haven assets due to mounting uncertainty stemming from the Middle East war.

The Wall Street brokerage cut its rating on global equities to "equal weight" from "overweight", while raising US Treasuries and cash to "overweight" from "equal weight."

"Uncertainty around magnitude and duration of oil supply disruption means outcomes for risk assets have become increasingly asymmetrical," Morgan Stanley strategists said in a note on Friday.

Brent has soared 59 per cent this month, its steepest monthly jump, exceeding gains seen during the 1990 Gulf War. Futures climbed above $116 a barrel on Monday.

The brokerage warned that if oil prices stay at around $150-$180 per barrel, global equity valuations could shrink nearly 25 per cent.

The firm has trimmed its overall equity exposure through a downgrade in US and Japanese stocks to "equal weight" from "overweight".

"We turn equal weight on Japanese stocks given negative tail risks as we expect it to come under pressure from supply chains and global recessionary impacts in a scenario where the Strait (of Hormuz) remains closed for longer," the strategists said.

Still, Morgan Stanley retained a preference for US stocks compared to other regions, given higher earnings-per-share growth.

US assets emerging as a safe haven again?

The shift stands in sharp contrast to most of last year, when investors shunned U.S. assets due to tariff-related uncertainties and rotated cash to European, Japanese and emerging market assets.

Fund flows to US equities and bonds have overtaken the rest of the world since the Middle East conflict began last month, with investors "looking to US assets as a more defensive market again," Morgan Stanley said.

In an oil supply shock, US Treasuries offer better diversification as the country is less energy import-dependent than Europe, the strategists added.