The United States has imposed sanctions on seven Pakistani companies over suspicions that they have engaged in nuclear trade.
The move could potentially damage Pakistan's ambition to join the Nuclear Suppliers Group (NSG), a group of countries that can trade nuclear technologies.
Relations between the United States and nuclear-armed Pakistan have been strained in recent years over Islamabad's alleged support for militant groups fighting Afghan and U.S. forces in Afghanistan. Pakistan denies the claims.
The U.S. Bureau of Industry and Security imposed the sanctions on the Pakistani companies on March 22 by placing them on its "Entity List."
The bureau said in a report that the Pakistani companies had been "determined by the U.S. government to be acting contrary to the national security or foreign policy interests of the United States."
Companies placed on the entity list will not suffer asset freezes but will need special licenses to do business in the United States.
A total of 23 companies were added to the list last week, including 15 entities from South Sudan and one from Singapore.
Pakistan has a poor record on nuclear proliferation.
A U.N. nuclear watchdog said in 2008 that the network of Abdul Qadeer Khan, known as the father of Pakistan's atomic bomb, smuggled nuclear weaponization blueprints to Iran, Libya, and North Korea and was active in 12 countries.
Based on reporting by Reuters and Dawn