The United States on Thursday urged China to be more transparent in its trials in the Xinjiang region as courts handed down more death sentences over last year's deadly ethnic unrest. The State Department voiced disappointment that China did not agree to US requests to observe the court proceedings. 'We continue to urge China to handle their detention and judicial processes in a more transparent manner,' State Department spokesman Philip Crowley told reporters. 'It's hard to comment on the specific merits of the case without having been in the courtroom to observe firsthand,' he said. A court in the western region Monday sentenced four more people to death, bringing to 26 the number of people who have been reported executed or condemned to die over their roles in the unrest, some of the worst ethnic violence in China in decades. Based on names provided in state media reports, most of those sentenced to death or executed have been Uighurs -- a mostly Muslim group that has often complained of discrimination from China's majority Han community. Violence erupted in July in the regional capital Urumqi that pitted Uighurs against Hans, leaving nearly 200 dead and over 1,600 injured. China says it faces a serious separatist threat in Xinjiang and has vowed harsh retribution for those found guilty of wrongdoing in the unrest. Exiled Uighurs say more people may have died and accuse China of exaggerating the separatist threat to justify control over the strategic western region, which is rich in energy reserves. 