"What the Russian leadership has done in Crimea is in clear contravention of international law," said Jean-Claude Juncker in an interview with the German broadcaster Deutschlandfunk. The former prime minister of Luxembourg, currently the leading election candidate of the conservative bloc in the European parliament, did not mince his words. "This does not constitute abiding by the obligations that the Russian leadership made in the 1990s with regard to Ukraine and Crimea," he said.

German Chancellor Angela Merkel seems to agree. The deputy spokesman for the German government, Georg Streiter, confirmed that Merkel had accused Russian President Vladimir Putin over the phone of conducting an "unacceptable Russian intervention in Crimea."

The United Nations Charter, which forms the basis for international law, forbids countries from starting wars of aggression. Russia, however, is convinced that military intervention across its border does fall under international law. Putin has justified sending soldiers to Crimea on the grounds that the lives of Russian compatriots are in danger.

However, Stefan Talmon, a professor of international law at the University of Bonn, argues that Putin is wrong. "There is no circumstance under international law in which it is permissible to send armed troops into another country to protect sections of the population there," he said.

http://www.dw.de/crimea-a-breach-of-international-law/a-17483425