Four people have been charged over leaks as the Trump administration launches a crackdown on embarrassing disclosures, the US attorney general has said.

Jeff Sessions said the administration has tripled the number of active leak investigations since the beginning of 2017.

He said the suspects were accused of divulging classified material or concealed contacts with foreign intelligence officers.

Mr Sessions, who has been accused by President Trump as “very weak” on leaks, said no government could be effective when its leaders could not talk freely in confidence with foreign leaders.

"[I] condemn in the strongest terms the staggering number of leaks undermining the ability of our government to protect this country," he said.

Mr Sessions admitted there had been a "dramatic" increase in recent months of unauthorised disclosures.

In a threat to press freedom, the attorney general also indicated he wanted to review policies on media subpoenas in a bid to make it easier to force reporters to reveal their sources