US President Donald Trump announced Monday that US special forces had captured a man linked to the 2012 attack on the American mission in Benghazi.

"Yesterday, on my orders, United States forces captured Mustafa al-Imam in Libya," Trump said in a statement, which came as the White House was rocked by the indictment of three campaign aides.

Trump said the capture took place "on my orders" and, as a result, "al-Imam will face justice in the United States for his alleged role in the September 11, 2012 attacks in Benghazi."

The attack killed ambassador Chris Stevens as well as three other American personnel and became emblematic of conservative opposition to then secretary of state Hillary Clinton.