LONDON, April 20 (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 LCOc1 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 ESc1 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.