MOSCOW (AP) — A doctor for imprisoned Russian opposition leader Alexei Navalny, who is in the third week of a hunger strike, says his health is deteriorating rapidly and the 44-year-old could be on the verge of death. Physician Yaroslav Ashikhmin said Saturday that test results he received from Navalny’s family show him with sharply elevated levels of potassium, which can bring on cardiac arrest, and heightened creatinine levels that indicate impaired kidneys. He wrote “our patient could die at any moment,” on a Facebook post. Anastasia Vasilyeva, head of the Navalny-backed Alliance of Doctors union, said on Twitter that “action must be taken immediately.” Navalny’s personal physicians have not been allowed to see him in prison.