By Sophie Kiderlin

(Reuters) - Oil prices jumped and global equities pulled back on Monday as markets grew increasingly concerned that the ceasefire between the U.S. and Iran might not hold, while tensions over the Strait ​of Hormuz escalated.

Brent crude futures rose about 5% to $94.92 a barrel. MSCI's world share index (.MIWO00000PUS) was last down around 0.26%, with Europe's cross-regional ‌STOXX 600 (.STOXX) down 1.1%, after Asia's equity markets shrugged off risks to advance. S&P 500 futures were 0.54% lower.

Concerns grew on Monday that the ceasefire between the United States and Iran might falter after the U.S. said it had seized an Iranian cargo ship that tried to run its blockade and Iran vowed to retaliate.

The U.S. has maintained a blockade ​of Iranian ports, while Iran has lifted and then reimposed its own blockade on marine traffic passing through the Strait of ​Hormuz.

Shipping traffic through the strait remained at a virtual standstill on Monday with just three crossings in the space of 12 ⁠hours, according to shipping data. Kpler data showed that more than 20 vessels carrying oil products, metals, gas and fertiliser had passed through the strait on Saturday, ​the busiest day for the chokepoint since March 1.

"Markets try to cling on to every bit of news that may point to one outcome or ​another, hence these large swings. But it is still a very uncertain and volatile situation," Sandra Horsfield, economist at Investec, said.

She noted that while markets have pulled back, moves made Friday - when Iran said it would open the Strait of Hormuz - had not been fully retraced, suggesting that at least some "improved sentiment still prevails".

Outside the Middle ​East, British Prime Minister Keir Starmer is slated to address Parliament on Monday, facing calls for his resignation over his handling of the appointment of ​Peter Mandelson as U.S. ambassador even though Mandelson had failed a vetting process. 

PEACE TALKS IN QUESTION; FOCUS ON HORMUZ

Visitors walk past screens displaying current market information at Japan Exchange Group's Tokyo Stock Exchange in Tokyo, Japan, April 6, 2026. REUTERS/Issei Kato

Meanwhile, the outlook for further negotiations between the U.S. ‌and Iran ⁠seemed uncertain.

"Whether this impasse proves to be merely a detour on the path to a resolution remains to be seen, but more volatility would seem the most likely outcome," Derren Nathan, head of equity research at Hargreaves Lansdown, said in a note.

Iran rejected new peace talks with the U.S., its state news agency reported on Sunday, hours after U.S. President Donald Trump said he was sending envoys for talks in Pakistan and would launch new ​strikes on Iran unless it accepts ​his terms.

"We always thought there ⁠would be some swings and roundabouts within that, rather than a straight linear path to the end outcome," said Investec's Horsfield.

Bonds, which rallied on Friday, retreated and the yield on benchmark 10-year Treasuries rose 2.4 basis points to ​4.2678%, while the yield on German 10-year government bonds was last 2.9 bps higher at 2.9947%.

The dollar - which was ​sold for the ⁠best part of the past two weeks - broadly steadied, trading at $1.1773 per euro.

Wall Street indexes (.SPX) touched record highs on Friday, supported by expectations of robust first-quarter

British inflation data, U.S. retail sales and European Purchasing Managers' Index figures are also due through the week, though much ⁠of markets' ​focus will be on Gulf shipping.

"The critical barometer of geopolitical risk has been distilled into ​one data point: The number of ships transiting the Strait of Hormuz," said Bob Savage, head of markets macro strategy at BNY.

"Peace talks matter, but the immediate focus is on ​oil and other supply shortages driving inflation."