Of the 10 terrorist attacks in the USA since 9/11, the countries of birth of the perpetrators were:
United States: 7 
Russia: 1 
Kyrgyzstan: 1 
Egypt: 1 
Kuwait: 1 
Pakistan: 1
That means 0 from Iran,  0 from Libya, 0 from Somalia, 0 from Sudan, 0 from Syria, and 0 from Yemen.
The 9/11 hijackers were from Saudi Arabia (15), United Arab Emirates (2), Egypt (1), and Lebanon (1).  Again, that means 0 from Iran,  0 from Libya, 0 from Somalia, 0 from Sudan, 0 from Syria, and 0 from Yemen.
What do you mean by "worst sources of terrorism"?