It does.

If you look at the list of Specially Designated Nationals and Blocked Persons, as published by the Department of the Treasury, you can find a number of US citizens, people with US passports or Social Security Numbers, and businesses registered in the US.

You can do that by searching the document for "citizen United States" to find US citizens or "(United States)" to find US businesses, passports and SSNs.

Under each entry you can find a tag (like [SDGT]). Together with this list you can check under which program a particular person was sanctioned.

As for the legality, I looked at 2 sanction regulations that involve a lot of US citizens.

1. [SDNTK] - Foreign Narcotics Kingpin Sanctions Regulations, 31 C.F.R. part 598, According to Section 598.314 this is limited to foreign persons engaged in drug trafficking, which are citizens or nationals of foreign countries, which may or may not be US citizens or nationals (§598.304)
2. [SDGT]​- Global Terrorism Sanctions Regulations, 31 C.F.R. part 594​ has the same definition of foreign person and also includes any person that assist these foreign persons (See 594.201, specifically Subsection (a)(3))

In all cases I found for US citizens put on the list under these sanction programs, the persons in question are also listed as citizens, nationals or passport holders of other countries. So according to the law establishing the sanctions, they can be put on the list.

It does.

If you look at the list of Specially Designated Nationals and Blocked Persons, as published by the Department of the Treasury, you can find a number of US citizens, people with US passports or Social Security Numbers, and businesses registered in the US.

You can do that by searching the document for "citizen United States" to find US citizens or "(United States)" to find US businesses, passports and SSNs.

Under each entry you can find a tag (like [SDGT]). Together with this list you can check under which program a particular person was sanctioned.

As for the legality, I looked at 2 sanction regulations under which US citizens appear on the list:

1. [SDNTK] - Foreign Narcotics Kingpin Sanctions Regulations, 31 C.F.R. part 598, According to Section 598.314 this is limited to foreign persons engaged in drug trafficking. Foreign persons are citizens or nationals of foreign countries, which may or may not be US citizens or nationals (§598.304).
2. [SDGT]​- Global Terrorism Sanctions Regulations, 31 C.F.R. part 594​ has the same definition of foreign person and also includes any person that assist these foreign persons (See 594.201, specifically Subsection (a)(3)).

In all cases I found for US citizens put on the list under these sanction programs, the persons in question are also listed as citizens, nationals or passport holders of other countries. So according to the law establishing the sanctions, they can be put on the list.

It does.

If you look at the list of Specially Designated Nationals and Blocked Persons, as published by the Department of the Treasury, you can find a number of US citizens, people with US passports or Social Security Numbers, and businesses registered in the US.

You can do that by searching the document for "citizen United States" to find US citizens or "(United States)" to find US businesses, passports and SSNs.

Under each entry you can find a tag (like [SDGT]). Together with this list you can check under which program a particular person was sanctioned.

It does.

If you look at the list of Specially Designated Nationals and Blocked Persons, as published by the Department of the Treasury, you can find a number of US citizens, people with US passports or Social Security Numbers, and businesses registered in the US.

You can do that by searching the document for "citizen United States" to find US citizens or "(United States)" to find US businesses, passports and SSNs.

Under each entry you can find a tag (like [SDGT]). Together with this list you can check under which program a particular person was sanctioned.

As for the legality, I looked at 2 sanction regulations that involve a lot of US citizens.

1. [SDNTK] - Foreign Narcotics Kingpin Sanctions Regulations, 31 C.F.R. part 598, According to Section 598.314 this is limited to foreign persons engaged in drug trafficking, which are citizens or nationals of foreign countries, which may or may not be US citizens or nationals (§598.304)
2. [SDGT]​- Global Terrorism Sanctions Regulations, 31 C.F.R. part 594​ has the same definition of foreign person and also includes any person that assist these foreign persons (See 594.201, specifically Subsection (a)(3))

In all cases I found for US citizens put on the list under these sanction programs, the persons in question are also listed as citizens, nationals or passport holders of other countries. So according to the law establishing the sanctions, they can be put on the list.