The Obama administration revealed a series of executive actions aimed at reducing gun violence, including measures to restrict sales by unlicensed dealers on 4 January. President Obama is expected to announce the package of executive actions, which includes 10 separate provisions, on 5 January.

Individuals who engage in the business of selling firearms must get a federal firearms dealers licence and do background checks for all buyers, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) said. "The goal is keeping bad actors away from firearms," US Attorney General, Loretta Lynch said.

According to NBC News, federal law exempts those who sell guns occasionally from the licence requirement but the ATF will give sellers notice if they are engaging in actual business. The notices will be based on a number of factors, including whether they make money on the guns they sell, how quickly they sell the guns they acquire and in what quantity they sell the weapons.

"These rules will provide clear notice to those individuals who try to hide behind the hobby exception when they are selling for a profit of for a business," the attorney general said. White House adviser Valerie Jarrett added, "It doesn't matter where you conduct your business—from a store, at gun shows or over the Internet. If you're in the business of selling firearms, you must get a licence and conduct background checks."

The president is also expected to devote an additional $500m (£339.8m) in federal funds to treat mental illness. The Washington Post noted that the president could need congressional approval for that particular provision. Another provision will require firearms lost in transit between a manufacturer and a seller be reported to federal authorities.

The Federal Bureau of Investigations (FBI) will start the hiring process of over 230 additional examiners and other personnel to help process background checks 24 hours a day, seven days a week. The Post reported the ATF has also established a new investigation centre to track illegal gun trafficking online and is expected to devote $4m and additional personnel to the National Integrated Ballistics Information Network.

Obama, who will participate in a town hall at George Mason University on 7 December, released a message on Twitter late on 4 January. "The gun lobby may be holding Congress hostage, but they can't hold America hostage. We can't accept this carnage in our communities," the president tweeted. The message came as the workers at the site of the San Bernardino massacre returned to work for the first time since the deadly shooting.

As expected, Republicans have blasted the president for his proposed measures. House Speaker Paul Ryan released a statement saying that without knowing the details of the plan, "the president is at minimum subverting the legislative branch, and potentially overturning its will....This is a dangerous level of executive overreach, and the country will not stand for it."