Credit: Frank Franklin II/AP Photo

The Treasury Department's Office of Foreign Assets Control, responsible for enforcing economic and trade sanctions against Iran and Syria, is being hindered because it has been pared down to a "skeleton crew" by the government shutdown, a Treasury official tells ABC News.

"This massively reduced staffing not only impairs OFAC's ability to execute its mission, it also undermines [the Treasury Department's Office of Terrorist Financing and Financial Crimes] broader efforts to combat money laundering and illicit finance, protect the integrity of the U.S. financial system, and disrupt the financial underpinnings of our adversaries," according to the official, who asked not to be named.

The Treasury official's comments come as Iran sanctions are in the public eye. As the U.S. and Iran wade into diplomacy over Iran's nuclear program, Israeli Prime Minister Benjamin Netanyahu warned the U.S. in interviews and in his U.N. speech not to back away from sanctions.

Broadly, employees essential to U.S. national security have remained on the job, despite the federal shutdown. According to plans laid out by the Department of Justice, all FBI and DEA field agents and support staff are exempt from furlough and will remain at work, for instance.

So what's being affected? A Treasury official told ABC News, via email, that the office (OFAC) "is unable to sustain its core functions of: (1) issuing new sanctions designations against those enabling the governments of Iran and Syria as well as terrorist organizations, WMD proliferators, narcotics cartels, and transnational organized crime groups; (2) investigating and penalizing sanctions violations; (3) issuing licenses to authorize humanitarian and other important activities that might otherwise be barred by sanctions; and (4) issuing new sanctions prohibitions and guidance."

The Department of Homeland Security, meanwhile, is maintaining most of its security functions, such as border patrol, cybersecurity, Travel Security Agency travel screenings, TSA air marshals, Coast Guard maritime security, and port security, according to its shutdown plan-pretty much everything you'd think to worry about, in terms of security-related federal employees.

Agencies have exempted from furlough employees whose jobs relate to the safety of life and property. The White House did not publish shutdown plans for CIA and NSA.

But Treasury's offices responsible for combating terrorist finances and financial crimes have been scaled back by the shutdown, too, the official said.

Treasury's Office of Terrorist Financing and Financial Crimes (TFI)-the department's arm that implements strategies to "combat terrorist financing domestically and internationally," according to its online description-and Treasury's Office of Intelligence and Analysis and the Financial Crimes Enforcement Network are also working with a "skeleton crew," the Treasury official said.