The US Senate’s top Republican has backed a probe into allegations the Kremlin engaged in a hacking campaign to influence November’s election in the most serious break yet between president-elect Donald Trump and his party’s traditional Washington leaders.

Mitch McConnell, Senate majority leader, said Congress would investigate the allegations following the disclosure of a Central Intelligence Agency report which concluded that Russia hacked into Democratic National Committee servers in an effort to sway the election outcome in Mr Trump’s favour.

The president-elect, who has dismissed claims of Russian interference and belittled the CIA after the conclusions became public, took to Twitter yesterday to insist it was “hard to determine who was doing the hacking”.