Signs that talks between US and Iranian officials may succeed could lower oil prices, traders said, after US and Brent crude reached multi-year highs on Friday.

If agreement is reached in Vienna to revive the 2015 nuclear agreement (JCPOA) with Iran and the United States lifts sanctions, it could boost oil shipments, adding about one million barrels a day to global supply.

Oil prices have risen sharply in past few months, nearing the important $100 pb threshold not seen since November 2014.

"There has been speculation that this rally was going to encourage some sanctions relief and get more Iranian oil on the market," John Kilduff, partner at Again Capital LLC in New York told Reuters.

On Friday, the United States restored sanctions waivers allowing international nuclear cooperation with Iran on projects designed to make it harder for Iran's nuclear sites to be used to develop weapons.

"President (Joe) Biden still wants us to negotiate in Vienna ... That's a symbol or a sign of our continued belief that it is not a dead corpse, that we need to revive it because it is in our interest," Rob Malley, U.S. envoy for Iran, told MSNBC Sunday night.

Iran on Monday demanded full removal of all sanctions imposed since 2018 when for US president Donald Trump withdrew from JCPOA.