Bristling with anger, President Barack Obama branded Wednesday's defeat of his gun reform drive in the U.S. Senate as "shameful," and accused lawmakers of caving in to the powerful firearms lobby.

A deeply emotional Obama lashed out after a bid to expand background checks for gun buyers, the last meaningful piece of his trimmed effort to retool gun laws after the Newtown school massacre, failed to pass.

Ringed by dazed and grief-stricken relatives of some of the 20 children gunned down in Connecticut in December, Obama accused the firearms lobby of lying to thwart change but vowed he would not give up the fight.

The president hinted that he would campaign on the issue in the 2014 mid-term elections.

Republicans argued that the bill infringed on the constitutional right to bear arms, but Obama said it did no such thing and merely tried to stop criminals and the mentally ill from getting firearms.

Some conservative Democrats, fearing a backlash as they run for re-election, also opposed the bill.AFP