The "commonsense" reforms, which bypass the Republican-controlled Congress, are opposed by critics, including Republican 2016 presidential hopefuls who argue that Obama's unilateral actions violate the US Constitution and restrict law-abiding citizens' access to firearms.

Here are key elements of Obama's executive actions:

1. Requiring background checks

The core of Obama's move involves firming up the existing system for conducting background checks on gun sales, notably by closing the "gun show loophole" which exempts dealers at gun shows or online from conducting a background check before selling a weapon.

2. Strengthening background check system

Authorities will act to make the National Instant Criminal Background Check System (NICS) more efficient, including improving state reporting to the system, hiring 230 more examiners to swiftly process checks around the clock, and modernizing digital aspects of NICS.