The package would include a strong statement backing the deal by European powers, together with efforts to lobby the U.S. Congress and put wider pressure on Iran, officials said.
But without strong U.S. support for the deal, senior officials in Berlin, Paris and London say it may be only a matter of time before the pact between Tehran and six world powers unravels, with grave consequences for Middle East security, nonproliferation efforts and transatlantic ties.
The two-year-old agreement, under which Iran agreed to freeze its nuclear program for 15 years in exchange for sanctions relief, is viewed in Europe as a rare triumph of international diplomacy in the Middle East.