None of the seven sanctioned Pakistani companies, which are not well known, could be immediately reached for comment, nor could a Singapore-based company which the bureau said was linked to one of the Pakistani companies.
Pakistani officials have in the past been accused of handing over nuclear secrets to North Korea. The government has denied the accusations though Pakistan has a poor record on nuclear proliferation.
The Pakistani scientist lionized as the father of Pakistan’s atomic bomb, Abdul Qadeer Khan, in 2004 said he had sold nuclear secrets to North Korea.
A U.N. nuclear watchdog said in 2008 that Khan's network smuggled nuclear weaponisation blueprints to Iran, Libya and North Korea and was active in 12 countries.
SANCTIONED COMPANIES
Of the latest companies to be sanctioned, Singapore-based Mushko Logistics and Pakistan-based Mushko Electronics "procured items for several Pakistani entities on the Entity List", the U.S. bureau said in its report.
Another company, Solutions Engineering, "has been involved in the procurement of U.S.-origin items on behalf of nuclear-related entities in Pakistan that are already listed on the Entity List".
Three of the companies - Akhtar & Munir, Proficient Engineers and Pervaiz Commercial Trading Co. (PCTC) - were on the list due to "involvement in the proliferation of unsafeguarded nuclear activities that are contrary to the national security and/or foreign policy interests of the United States".
Marine Systems was placed on the Entity list for helping other already-sanctioned bodies obtain items without a licence, while Engineering and Commercial Services (ECS) was sanctioned for "involvement in supplying a Pakistani nuclear-related entity on the Entity List".
The sanctions could deal a blow to Pakistan's application to join the NSG, a 48-nation club dedicated to curbing nuclear arms proliferation by controlling the export and re-transfer of materials that could foster nuclear weapons development.
Nuclear-armed Pakistan applied to join the NSG in 2016 but little progress has been made.
The United States has been concerned about Pakistan's development of new nuclear weapons systems, including small tactical nuclear weapons, and has been trying to persuade Islamabad to make a unilateral declaration of "restraint".
(Reporting by Drazen Jorgic; Editing by Robert Birsel)