By JAY SOLOMON
Updated July 21, 2015 7:59 p.m. ET

WASHINGTON—The Obama administration and European Union agreed as part of the accord last week to lift sanctions over eight years on a network of Iranian scientists, military officers and companies long suspected by the U.S. and United Nations as central players in a covert nuclear weapons program.

The U.S. also agreed to remove a German engineer from its financial blacklist by late 2023 after he was targeted by sanctions for his alleged role in a global black market in nuclear weapons technology run by the father of Pakistan’s nuclear program, Abdul Qadeer Khan.

The decision to roll back sanctions on these individuals and organizations is detailed in more than 100 pages of documents released last week as part of the landmark nuclear accord reached between Iran and six world powers.

The Obama administration decided to remove Gerhard Wisser from its sanctions list by 2023. The German engineer was convicted and sentenced to 18 years in prison by a South African court in 2007 for his role in supplying centrifuge components to the A.Q. Khan black-market network.

The intricate agreement is accompanied by five detailed annexes and technical attachments that spell out many of the long-term implications of the pact that lifts sanctions on Iran in exchange for curbs on its nuclear activities. Members of congressional staffs and outside Iran analysts said they’ve needed a week to begin understanding the finer details.

Republicans said in recent days they were stunned the White House and European allies agreed to lift sanctions on such individuals and expressed concerns about the long-term impact on U.S. and global security. A number of leading Republicans said the issue of sanctions relief will be among those they cite in attempting to block legislative approval of the Iran deal.

Congress started a 60-day review period of the agreement this week.

“This would remove sanctions on those responsible for Iran’s nuclear weapons development at the same time restrictions on Iran’s ballistic missile program come off,�? said Rep. Ed Royce (R., Calif.), chairman of the House Foreign Affairs Committee, referring to the delisting of Iranian scientists, companies and officers. “That’s a deadly combination.�?

Obama administration officials said the U.S. was required under the Vienna agreement and U.N. resolutions to lift sanctions on Iranian individuals and entities for their role Tehran’s nuclear program.

They stressed that they made sure to keep the sanctions in place for as long as possible, in some cases up to eight more years, before their repeal.

“Those resolutions always laid out a process that these sanctions would be removed if the concerns were addressed,�? said a senior U.S. official involved in the Vienna talks. “The sanctions were based on taking them off if the concerns were removed.�?

Among those to be removed from the U.S., U.N. and EU sanctions lists by 2023 is Mohsen Fakhrizadeh-Mahabadi. U.S. and Israeli intelligence agencies suspect he oversaw a secret Iranian program to develop the technologies for a nuclear weapon, at least until 2003. He’s been called by American officials the “ Robert Oppenheimer�? of Iran’s nuclear efforts, a reference to the American scientist who oversaw development of atomic weapons during World War II.

The U.N.’s nuclear watchdog, the International Atomic Energy Agency, has repeatedly attempted to interview the military officer to conclude its investigation into Tehran’s alleged weaponization work, but has repeatedly been rebuffed.

Iran denies it sought to build a bomb and has guarded access to its military sites and leadership.

“Some people in Iran will be very happy about this�? delisting, said Olli Heinonen, the former chief of the IAEA’s inspection arm who repeatedly attempted to interview Mr. Fakhrizadeh in the 2000s.

The U.S., U.N. and EU also committed in Vienna to remove Fereidoun Abbasi-Davani, a prominent Iranian nuclear scientist, from their sanctions lists over the next eight years.

The U.N. Security Council blacklisted Mr. Abbasi-Davani in 2009 for allegedly being a close aide to Fakhrizadeh and working on Iran’s nuclear and ballistic missile programs. The scientist then narrowly avoided an assassination attempt the next year in northern Tehran, for which he blamed Israel. Mr. Abbasi-Davani was promoted to head the Atomic Energy Organization of Iran from 2011-2013.

The military body Mr. Fakhrizadeh allegedly headed, the Organization of Defensive Innovation and Research, known as SPND, also will be removed from the U.S. sanctions list by 2023. The IAEA has said SPND may have been involved in nuclear weapons research after 2003. The agency has sought to interview officials from the organization but have also been rebuffed.

A spokesman for Iran’s foreign ministry did not respond to a request for comment on the sanctions involving the Iranian officials and institutions.

The Obama administration will begin briefing Congress on Wednesday, including with appearances by Secretary of State John Kerry.
Mr. Kerry and other administration officials have in some cases added to the confusion over the status of Iranians and others on sanctions lists. According to the Vienna documents, the commander of Iran’s overseas military unit known as the Qods Force will be taken off EU and U.N. sanctions lists in the next eight years. But the secretary of state initially denied that the commander, Maj. Gen. Qasem Soleimani, would be removed from sanctions lists. He will remain on U.S. sanctions lists.

Lawmakers and nuclear experts were also puzzled by the Obama administration’s decision to remove Gerhard Wisser from its sanctions list by 2023. The German engineer was convicted and sentenced to 18 years in prison by a South African court in 2007 for his role in supplying centrifuge components to the A.Q. Khan black market network.

The U.S. and IAEA accuse Mr. Khan and his associates of facilitating the sale of nuclear equipment to North Korea, Iran and Libya during the 1980s and 1990s.

The senior U.S. official didn’t provide specifics about why Mr. Wisser was granted sanctions relief as part of the Iran deal. Mr. Wisser could not be located. He pleaded guilty in 2007 in South Africa to manufacturing components that could be illegally used in nuclear technology.

Other non-Iranian individuals who procured equipment for Tehran also were delisted.

The U.S. also agreed to remove Kalaye Electric Co. from its sanctions list over the next eight years. The Iranian company was exposed by the IAEA as having secretly run a uranium-enrichment facility in the early 2000s.

The EU and U.N. also committed to removing Malek Ashtar University from their sanctions lists. The Tehran research center was accused of supplying scientists who participated in secret weaponization work, according to former U.S. and IAEA officials.