WARSAW—Authorities in Poland and the U.S. are probing the deep ties Beijing has forged in this strategically important country on NATO’s eastern frontier in the wake of high-profile arrests of a Chinese executive and a former Polish official.

Wang Weijing, who worked in Poland for Huawei Technologies Co., and Piotr Durbajlo, a former senior Polish counterintelligence official, were detained this month and charged with spying for China. Mr. Wang, who was fired by Huawei following his arrest, issued a statement via his lawyers...