ICA is Singapore's first line of defence against potential terrorist threats by restricting the movement of security sensitive persons across international borders. ICA also works closely with other agencies such as the Police and ISD to prevent terrorist attacks from occurring in Singapore. After the escape of Mas Selamat in 2008, all checkpoints immediately stepped up security checks. During the lead-up to the 2018 Trump-Kim Summit, Home Affairs Minister K. Shanmugam revealed that four people had been turned away at the checkpoints for terrorism related reasons.