US President Donald Trump has hit out at key allies over trade policy as leaders hold talks at the G7 summit in Canada. He is standing firmly on his newly imposed steel and aluminium tariffs with tensions threatening to overshadow the meeting. Mr Trump has also called for Russia to be reinstated to the group, after the country was ousted from the then-G8 summit in 2014 as punishment for President Vladimir Putin's annexation of Crimea and support for pro-Russian separatists in Ukraine.