That agreement, along with recent comments from Saudi officials and royals, is raising concerns on Capitol Hill and among U.S. allies that a deal with Iran, rather than stanching the spread of nuclear technologies, risks fueling it.

Saudi Arabia’s former intelligence chief, Prince Turki al-Faisal, a member of the royal family, has publicly warned in recent months that Riyadh will seek to match the nuclear capabilities Iran is allowed to maintain as part of any final agreement reached with world powers. This could include the ability to enrich uranium and to harvest the weapons-grade plutonium discharged in a nuclear reactor’s spent fuel…

The memorandum of understanding between Saudi Arabia and South Korea includes a plan to study the feasibility of building two nuclear reactors worth $2 billion in the Arab country over the next 20 years, according to Saudi state media.

Current and former U.S. officials said there is particular concern about Saudi Arabia’s decadeslong military alliance with Pakistan, a nuclear-armed state with a history of proliferating military technologies.