Italian jewellery and luxury goods maker Bulgari said on Friday it had asked its suppliers to certify that their jewels did not come from Myanmar.

“Even though the company has never bought stones directly from Myanmar, but only on the international markets, it has expressly asked its suppliers for guarantees on the geographical origin of their precious stones,” Bulgari said in a statement.

Myanmar’s military government last month violently suppressed the largest protests against its rule in nearly two decades, unleashing bullets and tear gas in the commercial hub Yangon and killing at least 13 people.

The move by Bulgari, the world’s third-biggest jeweller, follows a similar one from French jewellers Cartier, a subsidiary of Switzerland’s Richemont, and by US company Tiffany which itself stopped buying Myanmar jewels in 2003.

One of the poorest countries in the world, Myanmar supplies up to 90 percent of the world’s rubies and has rich jade deposits that are highly prized in neighbouring China.

Despite sanctions on the regime, many stones from Myanmar are smuggled through neighbouring Thailand, where they are often cut and polished for eventual sale in the United States or Europe.

For the past 700 years, the so-called “Valley of Rubies” in the Mogok region of northeast Myanmar has been mined for “pigeon blood” rubies — considered the finest in the world — as well as for sapphires and other rare gems.

The stones are mined at a huge human cost, with reports of horrific working conditions in Myanmar’s ruby mines, which outsiders are forbidden to see.