The US and the EU use international law in their war against Russia. This is proved by a number of cases, e.g. the case of YUKOS, the decision on Litvinenko, the MH-17 investigation, the scandal about Russia being the host of FIFA’s World Cup in 2018, etc.
YUKOS: the International Court of Justice (ICJ) is the principal judicial organ of the United Nations (UN), neither the US nor the EU has authority over its judgements. // Litvinenko: there is compelling evidence that the Russian state was behind Litvinenko's assassination on British soil which is a violation of the UK's sovereignty. (bit.ly/1WwPxYU), . // MH-17: the investigation into the shooting down of flight MH17 was carried out by the Dutch safety board, over which the US and the EU have no authority (bit.ly/1PdSc90), . // FIFA: In May 2015 Swiss prosecuting authorities launched a criminal inquiry on "suspicion of criminal mismanagement and of money laundering" concerning the 2018 and 2022 bidding processes (bbc.in/1QwP57q), .