UN Secretary-General Ban Ki-moon on Sept. 3 questioned the legality of the US plan to strike Syria. Ban stated  that the use of force is lawful only in two very limited circumstances: (1) when used in self-defense according to Article 51 of the UN charter or (2) when the UN Security Council (UNSC) approves such action. Ban questioned whether the planned use of force would solve the situation in Syria, adding that such use would cause more damage. Ban noted that UN inspectors are deployed to investigate whether chemical weapons have been used in Syria. According to Ban, the UNSC would be able to overcome its differences and take action once investigations are done. A potential US strike has been opposed by Russia. President Vladimir Putin on on Sept. 4 warned the US and its allies to take any unilateral action. However, he stated that he may support the UN action once investigations confirm use of chemical weapons. 

From Jurist, Sept. 4.