I believe the US knew this was coming:

On January 12, the United States unveiled sanctions against Khan, 12 associates and three firms linked to his nuclear proliferation network.
The sanctions forbid the 16 people and firms from having business dealings with the US government or private US companies in what the State Department says is a renewed bid to make sure the network has been shut down entirely.
A State Department official told AFP on the condition of anonymity that Washington has had concerns that elements of the network could still be active.

news.yahoo.com