Thi launched a coup attempt against President Diêm, but after surrounding the palace, they stopped attacking and decided to negotiate a power-sharing agreement. Diêm falsely promised reforms, allowing time for his loyalists to come to the rescue. The rebels had failed to seal the highways into the capital to block loyalist reinforcements. Khiêm was a Roman Catholic with ties to Diêm's older brother, Archbishop Thục; Diêm was also Khiêm's godfather. Khiêm brought in tanks from the Second Armored Battalion from Mỹ Tho, a town in the Mekong Delta, south of Saigon. As the false promises of reform were being aired, Khiêm's men approached the palace grounds. Some of the rebels switched sides as the power balance changed. After a brief but violent battle that killed around 400 people, the coup attempt was crushed. Khiêm was made a brigadier general after serving as the head of the 21st Division, and was appointed Chief of Staff of the combined armed forces and made a major general in December 1962. 1963 coup against Diệm One of Khiêm's subordinates, Phạm Ngọc Thảo, a Communist double agent, was planning one of the many coup plots that engulfed Saigon and destabilised the regime, with the help of Trần Kim Tuyến. Thảo's plans were shelved when an American CIA agent, Lucien Conein, instructed Khiêm, to stop the coup on the grounds that it was premature. Thảo was actually a communist double agent whose involvement in the plotting is generally attributed to cause infighting within the ARVN whenever possible. He later joined the main plot, of which Khiêm was part. As Diêm was known for his ability to outwit coup plotters, those in the plot did not fully trust each other. On the morning of the coup, an emotional Khiêm approached General Tôn Thất Đính with tears welling in his red eyes and asked him to keep their conversation confidential. After the III Corps commander agreed, Khiêm claimed he wanted to cancel the coup, saying "Đính, I think we still have time to talk to the old man. I don't want to hurt him. Have pity on him!" Đính contemplated the situation and said that he would proceed. Khiêm then reported this to Đôn, and claimed that he had placed Chinese medicinal oil into his eyes to irritate and redden them and thus give the appearance he had become remorseful about the coup, in order to test Đính's