LONDON—Oil slipped towards $90 a barrel on Tuesday ahead of the resumption of indirect talks between the United States and Iran, which could revive an international nuclear agreement and allow more oil exports from the OPEC producer. A deal could return more than 1 million barrels per day (bpd) of Iranian oil, equating to more than 1 percent of global supply, to the market. The nuclear talks are due to resume in Vienna on Tuesday. “If sanctions against Iran are lifted, global crude oil supply may receive much-needed support,” said Naeem Aslam, chief market analyst at Avatrade. Eight rounds of indirect talks between Tehran and Washington since April have yet to result in an agreement on a resumption of the 2015 nuclear pact, with differences remaining over the speed and scope of the lifting of sanctions. “Exports could resume swiftly if a nuclear deal is reached,” said Tamas Varga of …