The U.S. on Monday imposed its second round of sanctions in less than a week on people and firms in Africa who it says have provided financial or material support to the Islamic State group.

The latest financial penalties target South African entities, including one cell leader, Farhad Hoomer, accused of expressing "the will and intent to attack the interests of the United States," the Treasury Department said in a statement. Last week, the U.S. sanctioned what it said was a Somali Islamic State weapons trafficking cell.

Government reports outline how the Islamic State group is expanding its presence in Africa, after the group faced defeats in Iraq and Syria. The State Department has designated nine groups worldwide as IS affiliates and foreign terrorist organizations.

In the latest action, Treasury's Office of Foreign Assets Control designated four people and eight companies controlled by individuals that it said were in the South African Islamic State cell — including Nufael Akbar, Yunus Mohamad Akbar, Mohamad Akbar, and Umar Akbar. Their gold trading, construction and other firms are targeted for sanctions.

The move freezes and blocks any potential transactions with U.S. entities and prevents Americans from doing business with them.

State Department spokesperson Ned Price said in a statement that "as part of the Global Coalition to Defeat ISIS, the United States will continue to partner with South Africa to deny ISIS the ability to exploit the country's economy to raise and transfer funds in support of ISIS terrorist activities."

The Islamic State group sometimes is known as the Islamic State of Iraq and Syria, or ISIS.

The Treasury Department last week issued financial and diplomatic sanctions against a weapons trafficking network affiliated with the Islamic State group in Somalia and the al-Qaida-linked al-Shabab extremist group, which are accused of carrying out deadly terrorist acts on civilians including car bombings.

Treasury Under Secretary for Terrorism and Financial Intelligence Brian Nelson said the sanctions target "key individuals in ISIS's network in South Africa, as well as their business assets, who have played pivotal roles in enabling terrorism and other criminal activities in the region."