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
More than a million adults in the UK may have been wrongly diagnosed with asthma, according to an NHS watchdog.
A whisky advert featuring David Beckham has been cleared by the advertising regulator.
Councils will have to cut money from services such as libraries because of the rising cost of caring for the elderly, a new report warns.