WallStreetJournal--  The U.S. and three European countries will begin formal talks as early as next week on what the Trump administration considers flaws in the 2015 Iran nuclear agreement, but Secretary of State Rex Tillerson said they might not meet a White House deadline for a fix.

Donald Trump said earlier this month he wouldn’t renew U.S. sanctions relief to Iran in May, as required under the nuclear accord, unless Europe goes along by then with a supplemental agreement to restrict Iranian missile testing and development, provide for expanded inspections and extend prohibitions on nuclear-weapons work.

“The U.S. is under a bit of a timetable to deliver on what the president is looking for. But we can’t set timetables for others,” Mr. Tillerson told reporters traveling with him on Monday, on a flight from London to Paris.

Mr. Tillerson didn’t provide many details, but said diplomats from the State Department would travel to Europe as early as next week to discuss a side arrangement with officials from Germany, France and the U.K.

“It’s all being worked on as a package because that’s the way we’re going to have to deal with it ultimately,” he said.

Iran, Russia and China have opposed changes to the nuclear agreement. U.S. officials say any new agreements on additional sanctions wouldn’t require buy-in from other parties to the nuclear deal, because they are outside of the 2015 accord and would likely entail sanctions not related to it.

Mr. Tillerson is set to meet Mr. Le Drian Tuesday in Paris to discuss Iran, Syria and other issues ahead of a meeting on preventing the use of chemical weapons.