Global oil prices fell and rose again on Wednesday after US President Donald Trump said he would extend a ceasefire with Iran until peace talks between the two countries have progressed.
He added that the US will continue to blockade Iran's ports until Tehran presents a "unified proposal".
After opening higher in Asia, the global benchmark wholesale oil price dipped to $97.60 (£72.14) a barrel.
But the price rose again as reports of ships being attacked in the Strait of Hormuz emerged, with the price briefly hitting $100 a barrel before falling back slightly.
Energy markets have been volatile since the US and Israel attacked Iran on 28 February and Tehran responded with threats to target vessels in the key Strait of Hormuz waterway.
The initial two-week ceasefire had been due to expire on Wednesday evening Washington time. Trump did not give a new deadline for the ceasefire extension.
Trump said on Truth Social that the Iranian government has been "seriously fractured" and that the US will hold off from launching new attacks after Pakistan called for more time for Tehran to agree a deal.
Vice President JD Vance, who is leading the US negotiations, had been expected to fly to Islamabad in Pakistan for talks on Tuesday. The White House has now said he will not be going.
Iran has also not decided whether to send a delegation to Pakistan for talks with the US, a foreign ministry spokesperson told the BBC.
Traders remain cautious about what wil happen next in the war, said associate professor Jiajia Yang from Australia's James Cook University.
This is less about barrels [of oil] and more about expectations," Yang said.
The cost of crude has soared since the start of the conflict due to the Strait of Hormuz, through which a fifth of the world's energy usually passes, being effectively closed by Iran.