On 17 June 1969, US Senate Majority Leader Mike Mansfield, who had long been an advocate of normalizing American relations with China, wrote a letter in consultation with the White House to urge he to allowed to visit China and to meet Mao to discuss measures to improve Sino-American relations. The letter was sent to King Norodom Sihanouk of Cambodia with the request to pass it on to Mao, and by 26 July 1969, Mansfield's letter had arrived in Beijing. The Chinese reply was harsh, with Zhou giving a speech accusing the US of "aggression" in Vietnam and of "occupation" of Taiwan, which Zhou asserted was rightfully a part of China. On 1 August 1969, US President Richard Nixon visited Pakistan, a close ally of China since both were anti-Indian, to ask General Yahya Khan to pass a message to Mao that he wanted to normalize relations with China, especially because of the crisis with the Soviet Union.