The burgeoning Iran crisis has sparked oil supply worries over the Strait of Hormuz -- a vital shipping lane for a fifth of global crude -- and also over Iraq's output, analysts say.
Oil prices had surged last Friday after US President Donald Trump ordered the drone assassination of Iran's top general Qasem Soleimani, but the market stabilised on Monday and Tuesday with Middle East crude supplies unaffected.
However on Wednesday, the oil market shifted higher once more after Tehran launched revenge attacks to target US forces in Iraq, making good on its pledge to hit back over the killing.
Iran fired missiles overnight at Iraqi bases housing the US and British military, officials in Washington and Tehran said.
British Foreign Secretary Dominic Raab voiced concern over "reports of casualties".
But Iranian Foreign Minister Mohammad Javad Zarif insisted that the country does "not seek escalation or war".
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Traders remain fearful nevertheless that Tehran could seek to block the Hormuz waterway -- a key artery for crude that stretches between Oman and Iran.
Hormuz, one of the world's most congested transit points, links up the region's oil producers with markets in Asia, Europe and North America.
"Supply disruptions were put at the forefront of the agenda for investors," said Mihir Kapadia, CEO of Sun Global Investments.
"These concerns have been fuelled by Friday's killing of Soleimani and it is likely Iran will try and disrupt oil exports that travel through the Straits of Hormuz.
"However...it remains unclear as to what the next developments will be."