BRUSSELS, March 1 (Reuters) - The initial stage of a European Union and G7 ban on imports of Russia-origin diamonds via third countries came into effect on Friday, the Belgian government said in a statement.

The 27-member EU agreed to ban non-industrial Russian diamonds in December last year when it passed its 12th package of sanctions on Russia in response to its invasion of Ukraine in 2022. Belgium holds the EU's rotating presidency until the end of June.

A ban on direct imports of Russian diamonds began on Jan. 1 while the indirect ban will be phased in over a period of six months from Friday. The EU ban is in conjunction with the Group of Seven (G7) countries.

Rough and polished diamonds will have to enter the EU and G7 countries with documentary proof and declarations that the stones are not of Russian origin. From Sept. 1, a traceability mechanism will be added to the system.

Alrosa, Russia's biggest diamond producer, was also added to the EU's sanctions list in January. (Reporting by Julia Payne, Editing by William Maclean)