Mandela was called back from his African trip over concerns that he had been making black nationalist statements to win support – but which were contrary to the principle of non-racialism as set out in the Freedom Charter. Upon his return he paid a visit to Chief Luthuli, who was under banning orders in Groutville, to brief him on the outcomes of his trip. The South African Police received a tip-off from the American Central Intelligence Agency that Mandela was in Natal, and arrested him near Howick on 5 August 1962, on his way back from seeing Luthuli. On 7 November 1962, Mandela was sentenced to five years imprisonment for inciting workers to strike and for leaving the country illegally. MK explosions in Port Elizabeth and Durban demonstrated resistance to the sentence.