US President Donald Trump says Russia will pay a 'big price' for backing the Syrian regime's alleged use of chemical weapons. Washington is planning new sanctions to turn up the pressure on Bashar al Assad's closest ally. Shares in some of Russia's biggest companies and the rouble currency plummeted on the news. But as Liz Maddock reports, Moscow may retaliate with its own measures. TRT World’s Editor-at-large Craig Copetas joins us from Paris.