Source: Sharecast
The FTSE 100 was called to open around 0.6% lower. At 0725 BST, Brent crude was up 2.1% at $98.20 a barrel.
Danske Bank said: "The US conducted strikes on Iranian missile launch sites and mine-laying boats in southern Iran overnight, with Centcom citing self-defence. The attacks once again put the fragile ceasefire from April under pressure.
"This follows a weekend in which President Trump signalled the two sides were close to a deal, posting that talks were ‘proceeding nicely’."
The war in Ukraine was also in focus after Russia told the US to evacuate its diplomats and citizens from Kyiv.
In corporate news, DIY chain owner Kingfisher said it was still on track to meet full-year guidance despite a 0.9% fall in first-quarter sales due to softer markets in the UK and France.
Total sales for the three months to 30 April at the B&Q and Brico Depot owner came in at £3bn. Kingfisher said it expects FY 26/27 adjusted pre-tax earnings of £565m-£625m and free cash flow of £450m-£510m.
Government services provider Serco said it has successfully retained its facilities management contract at Norfolk and Norwich University Hospital.
Serco, which has delivered critical services at NNUH for 25 years, said the renewed agreement had a total value of more than £270m over the next 10 years and takes effect immediately.