But House of Representatives budget committee Chairman Paul Ryan argued that Republicans had made enough concessions.

BBC: Barack Obama unveils $3.77tn budget plan

Mr Romney has embraced the budget of Paul Ryan, the Republican chairman of the Budget Committee in the House of Representatives, which promises steep cuts in federal entitlements, including food stamps and Medicaid, and the replacement of traditional Medicare for the old with cheaper vouchers.

ECONOMIST: The size of the state

Mr Ryan chairs the budget committee in the Republican-controlled House of Representatives, and is seen as likely to add electoral firepower on what are expected to be the key election issues - jobs, the economy and the budget deficit.

BBC: Republican Romney names Paul Ryan as running mate