Asked about the US-UK extradition treaty which has been described as "one-sided", Attorney General Dominic Grieve QC said there were "underlying fundamental problems that are not very easy to address".
"I think there's a lack of public confidence in the US justice system," he said.
There were perceptions in Britain that the US justice and penal systems were "harsh and disproportionate", leaving Britons "uneasy and uncertain", he added.
He told the MPs these concerns were "not readily curable".
More top news
Warming up in the south but with breezy showers across Scotland today.
BA passengers face tighter curbs on the size of hand luggage as part of inclusive allowances for economy and premium economy travellers.
The wrestling hall of fame star 'Rowdy' Roddy Piper has died aged 61.