US authorities are to examine Roman Abramovich’s ties to the Kremlin as part of a national security review of a $2.3bn (£1.18bn) bid for Oregon Steel by a company controlled by the Russian billionaire.

Experts in Washington say the US government panel that reviews foreign deals will scrutinise the proposed takeover, announced last month, more closely if Mr Abramovich is found to be acting with the backing of the Russian government.