Sihanouk later claimed that the 1970 coup against him was the result of an alliance between his longstanding enemy, exiled politician Son Ngoc Thanh and Sirik Matak, with CIA support and planning. Although there are indications that Lon Nol approached the US during 1969 to gauge the likelihood of military support for a coup against Sihanouk, there is no concrete evidence of CIA involvement, though it remains possible some military intelligence agents may have had partial responsibility. It seems likely that in setting in motion the events leading up to the coup, Lon Nol initially intended to strengthen his position against the North Vietnamese with the ultimate aim of preventing their troops (and those of the Viet Cong) from operating within Cambodian borders, and wished to apply pressure on Sihanouk to achieve this. However, events rapidly developed far beyond the original plan, and with the encouragement of Sirik Matak – who wished to see Sihanouk deposed as Head of State – Lon Nol was ultimately to engineer Sihanouk's removal.