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The Obama administration, seeking to plug loopholes in its sanctions against Iran, said Thursday that it would impose additional measures against more than a dozen companies and people involved in that country’s nuclear and ballistic missile programs.

Among the companies designated by the Treasury are Electronic Components Industries and Information Systems Iran, which are subsidiaries of an entity that is, in turn, controlled by the Iranian Ministry of Defense. The companies work on semiconductors, circuit boards and mainframe computers that have both civilian and military uses.

Also on the blacklist are four men — three Iranians and an Austrian — that the Treasury Department said support Iran’s nuclear and missile programs. Under the sanctions, Americans are barred from doing business with these individuals, and any assets they have under American jurisdictions are frozen.

The administration identified energy-trading firms based in Switzerland, Hong Kong, Malaysia and Dubai that it said are either owned or controlled by or that carry out transactions on behalf of Iran’s national oil company.