Jay Inslee, Governor of Washington state, has signed legislation to prohibit dozens of semiautomatic rifles.
The bill bans the sale, transfer, distribution, manufacture and importation of 62 gun models it defines as "assault weapons", including AR-15s, AK-47s and similar high-powered rifles that have been used to carry out the mass shootings across the US, Xinhua news agency reported.
"These weapons of war, assault weapons, have no reason other than mass murder," Inslee said at the signing ceremony on Tuesday. "Their only purpose is to kill humans as rapidly as possible in large numbers."
The bill took effect immediately upon Inslee's signature.
Inslee also signed into law two other major gun measures, including a 10-day waiting period for gun purchases and a bill that would hold gunmakers liable for negligent sales.
The three gun bills passed the legislature on largely party line votes, with Republicans opposing them and most Democrats voting in support, according to a report by The Seattle Times.
The signing ceremony took place in the state Capitol, which was closed to the public on Tuesday morning out of security concerns.
The state of Washington joins nine other states, including California, Illinois, New York, Massachusetts, and New Jersey, as well as the District of Columbia, which have imposed bans on AR-15s and similar guns, according to the Giffords Law Center.