ISLAMABAD -- Pakistan’s drive against polio was thrown into disarray Tuesday after a foreign doctor working on a vaccination campaign was shot, a day after the Taliban reiterated a ban on immunization in the country’s tribal areas, officials said.

A three-day nationwide immunization program was launched Monday, but the Pakistani Taliban prohibited its administration in parts of the tribal area, the militant-infested zone that borders Afghanistan, putting about 280,000 children at risk. The doctor injured Tuesday, a Ghanaian employed by an arm of the United Nations, was working at the other end of the country, in the southern port city of Karachi, when gunmen sprayed his vehicle with gunfire in a poor district occupied mainly by ethnic Pashtuns.

Last year Pakistan was the country with the highest number of cases of polio, a crippling childhood disease that’s been eradicated in most of the world. A longstanding prejudice against anti-polio drops – many Pakistanis believe they’re a Western conspiracy to sterilize Muslims – has been fueled by the case of Shakil Afridi, a Pakistani doctor recruited by the CIA last year to help track Osama bin Laden.

There has been a worsening backlash against polio and other immunizations since McClatchy reported last July that the CIA had Afridi set up a fake vaccination program as a ruse to hunt bin Laden in the town of Abbottabad, which lies in the northwestern province of Khyber Pakhtunkhwa. Pashtuns, a conservative ethnic group, are the majority in that province and the tribal area.

“The Shakil Afridi factor has had an impact,” Shahnaz Wazir Ali, a senior adviser to the prime minister who is overseeing the polio eradication campaign, said in an interview. “Not all over Pakistan, but in certain parts, in Khyber Pakhtunkhwa, in the Pashtun community. Also in certain Pashtun communities in Karachi.”

In May, Afridi was sentenced to 33 years in jail, creating another hurdle in relations between Washington, which sees the doctor as a hero, and Islamabad, where he is viewed as a traitor for working secretly for a foreign intelligence agency.

On Thursday, Afridi’s case is due to go to appeal. But his lawyer told McClatchy that he hadn’t yet received the record of the evidence against his client.

Afridi was sentenced not by a court but in a secret trial by the administration of the tribal area under special laws that govern that region. His appeal will be heard behind closed doors by the city administration chief for Peshawar, the main city in the northwest.

In Washington, Sen. Rand Paul, R-Ky., plans to introduce a bill Friday that would cut off all U.S. aid to Pakistan – including $1.5 billion in annual civilian assistance and $1.2 billion in annual military aid – unless it frees Afridi.

Afridi had been tasked with trying to collect a DNA sample from the house where the CIA suspected bin Laden was living. A U.S. special forces team killed the al Qaida leader in that house in May 2011. Humanitarian aid groups across the world have condemned the use of a medical operation as cover for espionage.

Maryam Yunus, a spokeswoman for the U.N. World Health Organization, said that its vehicle came under attack around noon in Karachi. Men on two motorcycles shot at the tires to immobilize the vehicle and then turned their weapons on the people in the car, Yunus said.