South Korea's efforts to build an indigenous space launch vehicle have been marred due to persistent political pressure from the United States, who had for many decades hindered South Korea's indigenous rocket and missile development programs in fear of their possible connection to clandestine military ballistic missile programs, which Korea many times insisted did not violate the research and development guidelines stipulated by US-Korea agreements on restriction of South Korean rocket technology research and development. South Korea has sought the assistance of foreign countries such as Russia through MTCR commitments to supplement its restricted domestic rocket technology. The two failed KSLV-I launch vehicles were based on the Universal Rocket Module, the first stage of the Russian Angara rocket, combined with a solid-fueled second stage built by South Korea.