Olympia, Washington - Washington became the latest US state to prohibit sales of AR-15s and dozens of other semiautomatic rifles, as Governor Jay Inslee on Tuesday signed the ban into law, effective immediately.

The state Capitol was closed to the public Tuesday morning for the signing ceremony out of security concerns, though only a handful of protesters gathered outside.

"These weapons of war, assault weapons, have no reason other than mass murder," Inslee said at the ceremony in the ornate State Reception Room, flanked by lawmakers and people who'd lost loved ones to gun violence. "Their only purpose is to kill humans as rapidly as possible in large numbers."

The gun ban signed by Inslee, which stacks atop a bundle of gun restrictions adopted over the past several years in Washington, is aimed at high-powered rifles that have been used to carry out the worst mass shootings across the US.

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Inslee on Tuesday also signed into law two other major gun measures, including a 10-day waiting period for firearm purchases and a bill that would hold gunmakers liable for negligent sales.

Supporters of the ban and other restrictions in Washington said they will help prevent some mass shootings, or at least lower the death toll, while also reducing other gun violence and suicides.

Opponents called the ban an unconstitutional infringement of the rights of law-abiding gun owners and immediately filed a lawsuit seeking to have it struck down.

The federal lawsuit, filed by the Bellevue-based Second Amendment Foundation and other opponents, contends the law signed by Inslee "has criminalized one of the most common and important means by which its citizens can exercise their fundamental right to self-defense."

The lawsuit seeks a preliminary injunction barring enforcement of the ban.