They said the decision will take effect around the end of the year after the International Atomic Energy Agency (IAEA) certifies that Iran has met its commitments under a landmark July accord with the major powers to curb its nuclear programme in return for lifting sanctions.
"The EU will adopt the legislative framework for lifting all nuclear-related economic and financial sanctions but this will of course only apply ... Once the IAEA would have ticked all the boxes," one of the sources said.
Crucially, Iran will have to satisfy the IAEA, the UN nuclear watchdog, that it has taken the steps required to ensure its Arak reactor and other installations cannot be used for military purposes.
Sunday's announcement will complete the 90-day adoption stage of the July agreement reached between Iran and the five permanent UN Security Council members -- Britain, China, France, Russia and the United States -- plus Germany.
The sanctions have proved very damaging, locking up billions in Iranian assets overseas and starving the oil-dependent economy of crucially needed technology and investment.
Washington is expected to make a similar announcement Sunday on lifting its Iran sanctions.
