The FBI has arrested an Afghan man who officials say was inspired by the Islamic State militant organisation and was plotting an Election Day attack targeting large crowds in the US, the Justice Department said on Tuesday.

Nasir Ahmad Tawhedi, 27, of Oklahoma City, Oklahoma, told investigators after his arrest Monday that he had planned his attack to coincide with Election Day next month and that he and a juvenile co-conspirator expected to die as martyrs, according to charging documents.