The United States on Tuesday added South African twin brothers accused of plotting attacks on the US embassy and Jewish institutions to its terror blacklist.

Tony-Lee Thulsie and Brandon-Lee Thulsie were arrested in South Africa in July 2016.

Besides allegedly conspiring to bomb the US embassy in Pretoria and unspecified Jewish facilities they are also accused of planning to travel to Syria to join the Islamic State group.

Their arrests were the first in South Africa relating to alleged ISIS membership.

The State Department said that because of the threat they pose to US security the pair had been named “Specially Designated Global Terrorists”.

“These designations seek to deny Tony-Lee Thulsie and Brandon-Lee Thulsie the resources they need to plan and carry out terrorist attacks,” the State Department said in a statement.

“Terrorism designations expose and isolate entities and individuals, and deny them access to the US financial system,” it said.