The U.S. government has again bailed out Citigroup, unveiling a bold plan Sunday night to inject $20 billion in fresh capital into the troubled financial giant and shoulder most of the potential losses on $306 billion of high-risk assets.

Amid a flurry of government-backed steps to fortify the U.S. economy, Fed chief Ben Bernanke told lawmakers Tuesday the economy continues to face "numerous difficulties" including turbulent financial markets, rising unemployment and housing troubles.