New York's main contract, light sweet crude for December delivery fell 20 cents to USD 98.79 a barrel and Brent North Sea crude for December was 23 cents higher at USD 114.39.
"We think that the markets are just getting a little concerned over the supply side shock that could come if the matter escalated in some form or extent," said David Lennox, a Sydney-based resource analyst with Fat Prophets research house.
"We don't believe that it will. At this point, we are not too concerned," he told AFP. Israeli Prime Minister Benjamin Netanyahu yesterday called on world governments to waste no time in stopping "Iran's race to arm itself with a nuclear weapon."
The International Atomic Energy Agency (IAEA) said in its report last week there was "credible" intelligence suggesting Iran had carried out work towards building nuclear warheads, a claim denied by officials in Tehran.
Iran is the second-biggest producer in the Organization of the Petroleum Exporting Countries after Saudi Arabia, and any escalation in the standoff over its nuclear programme is seen as potentially disruptive to oil supply from the country.