(IDEX Online) - Police in Angola have seized a 147-carat diamond as part of Operation Transparency, its long-running crackdown on illicit diamond trafficking and illegal immigration.An Angolan citizen and a foreign national were detained in the eastern Lunda Norte province, according to the country's official news agency Angola Press. No further details about the stone were disclosed.Security forces forces seized 6,579 diamond stones last year, as well as 19 vehicles and $275,000. They also detained almost 150,000 illegal foreign citizens, the news agency said.Angola has made repeated efforts to counter diamond smuggling and faced ongoing allegations over "conflict diamonds".It's currently the world's sixth biggest diamond producer but has yet to explore 60 per cent of its potential kimberlite reserves.