DAR ES SALAAM, Tanzania — As one of the leaders of an acrimonious doctors’ strike in Tanzania, Dr. Stephen Ulimboka was not entirely surprised when a group of armed men appeared, unannounced, at a meeting and arrested him. But when he saw that the car they were forcing him into had no license plates, fear truly hit him.

A black hood was thrown over his head. “You’re going to pay for what you’ve been doing,” Dr. Ulimboka recalled one of the men saying. “You can start praying to your God because there is no turning back.”

They beat him for hours on that June night last year, first with their fists, then with metal rods. They pulled the toenails from both of his big toes. As he lay on the ground, he heard them discussing the best way to kill him: running him over with the car or giving him a lethal injection. He was unsure if he would live till daybreak.

Tanzania has a reputation abroad as an island of stability in the often-chaotic region of East Africa. The country has been rewarded with praise and money from international donors, including the United States, which last year gave the country more than $480 million.