China has yet to engage with U.S. officials over the cases of two Americans detained in the country, despite repeated personal appeals from President Donald Trump and what officials described as encouraging signals from Chinese President Xi Jinping, according to reports. 

The cases involve Youlin Chen, a seismologist who has been imprisoned for more than two years, and Min Zin, an academic who was arrested in June.

Sources familiar with the cases said China's lack of follow-through has been unusual, particularly after indications that Xi was receptive to discussing the Americans' situations.

Trump is expected to bring up both cases again when he meets with Xi on the sidelines of the Asia-Pacific Economic Cooperation (APEC) summit in Shenzhen, China, on Nov. 18 and 19. 

It would mark the third time Trump has raised Chen's detention and the second time he has addressed Min Zin's case, reports said.