A global arms trade treaty regulating the multibillion-dollar business has come into force - a move hailed as "a new chapter" by UN chief Ban Ki-moon.
He said he hoped the treaty would help prevent the transfer of weapons to "warlords, human rights abusers, terrorists and criminal organisations".
The deal also bans arms supplies if this promotes war crimes or genocide, reports the BBC.
So far 60 nations have ratified the accord, but not the US - the world's top arms exporter.
Washington signed the agreement in 2013, but now it requires approval by the Senate, where opposition is believed to be strong.
Other major weapons traders - like China, Russia, India and Pakistan - are yet to put their signatures under the deal.