Oil prices soared and stock markets came under pressure on Monday after intense US-Israeli strikes on Iran prompted fears of significant global economic disruption.

Brent crude jumped by as much as 13% during early trading – to hit $82 per barrel, a 14-month high – as the effective closure of the strait of Hormuz, one of the most important arteries for global trade, intensified concerns over oil supplies.

In Tokyo, the Nikkei 225 fell by nearly 2.4% as traders in Asia responded to the weekend’s developments. Pre-market trading also put Wall Street on course to open lower on Monday. In Sydney the ASX 200 opened down sharply, before recovering, to trade about 0.4% lower. Gold, often deemed a safe-haven asset by investors during times of crisis, rose 2.8% to $5,397.10 per ounce.

Military strikes by the US and Israel on Iran showed no sign of lessening, with Donald Trump suggesting the conflict could last for four more weeks and saying that attacks would continue until US objectives were met.

While oil fell back slightly from its initial highs, Brent remained up at least 7% during early trading.

As prices rallied, all eyes were on the strait of Hormuz – with about a fifth of oil supplies and seaborne gas tankers passing through it.

Within hours of Saturday’s US-Israeli strikes, Tehran had reportedly warned tankers in the strait that no ship would be allowed to pass through.

Two ships have been attacked in the strait, one off Oman and the other off the UAE, according to United Kingdom Maritime Trade Operations (UKMTO), the British maritime security agency.

While Iran has yet to officially confirm that the vital waterway has been blocked, marine tracking sites showed tankers piling up on either side of the strait wary of attack or maybe unable to get insurance for the voyage.

Maersk, the shipping multinational, announced on Sunday that it was halting passage through the strait of Hormuz and the Suez canal, another vital artery of the world economy, citing “safety” reasons.The Opec+ cartel of producing nations agreed a modest oil output boost of 206,000 barrels per day for April on Sunday, but a lot of that product still has to get out of the Middle East by tanker.

Iran is one of the cartel’s largest producers, pumping 4.5% of global supplies, so any disruption to its own shipments is likely to have an impact on the wider market.

“The most immediate and tangible development affecting oil markets is the effective halt of traffic through the strait of Hormuz, preventing 15m barrels per day of crude oil from reaching markets,” said Jorge León, the head of geopolitical analysis at Rystad Energy.

“Unless de-escalation signals emerge swiftly, we expect a significant upward repricing of oil.”

Reuters and AFP contributed to this report