This invasion not only provoked a Chinese attack on Vietnam in February 1979 but also posed a threat to Thailand's security. Chomanan could no longer rely on Cambodia as a buffer against Vietnamese power. Bangkok was forced to assume the role of a frontline state against a resurgent communist Vietnam, which had 300,000 troops in Cambodia and Laos. The Chomanan's government began increasing its defense capabilities. While visiting Washington in February 1979, Prime Minister Kriangsak Chomanan asked for and received reassurances of military support from the United States. His government also launched a major diplomatic offensive to press for the withdrawal of all Vietnamese forces from Cambodia and for continued international recognition of Democratic Kampuchea under Pol Pot's Khmer Rouge regime. As part of that offensive, Chomanan also journeyed to Moscow in March 1979, the first visit ever by a Thai prime minister. To explain the Thai position on the Cambodian question and to reassure the Soviets that Thailand's anti-Vietnamese position was neither anti-Soviet nor pro-Chinese. Such reassurances were believed to be necessary in view of Vietnamese accusations that Thailand collaborated with China and the United States in aiding and abetting the Khmer Rouge forces against the Heng Samrin regime.