U.S National Security Adviser John R. Bolton said on Monday he hopes Russia will reconsider its plans to sell S-300 missile defense systems to Syria as that would be a "significant escalation" by Moscow, Reuters reports.Pointing at Iran, Bolton claimed that it's that country which is responsbile for attacks on Syria and Lebanon, as well as downing the Russian plane in Syria. An incident that the Russian Ministry of Defense argued Israel is involved in and Israel denies, claiming it was downed by Syria.