Updated

Gunmen in the Pakistani city of Karachi opened fire Tuesday on a vehicle carrying a doctor working with the World Health Organization on an anti-polio campaign, wounding him in the stomach, the organization said.

The head of the World Health Organization's polio eradication program in Pakistan, Dr. Elias Durry, said the doctor is an international volunteer helping supervise the project. He said the man underwent surgery in Karachi.

Pakistan is in the middle of a campaign to vaccinate children under five. Taliban militants in northern Pakistan have barred the vaccination campaign from territory under their control, saying it can't go forward until the U.S. stops drone strikes in the country.

In a statement, WHO said the attack did not appear to be specifically targeting the doctor.

"At this point, there is no evidence to suggest that this was a deliberate or targeted attack against polio eradication efforts or WHO," the Geneva-based organization said. "WHO is grateful to the Pakistan authorities for launching an investigation into this event, to determine more clearly the circumstances."

Pakistan's largest city, Karachi has struggled for years with political and criminal violence.

Durry said despite the shooting WHO is committed to eliminating polio in Pakistan.

"This incident will not distract from the progress Pakistan is making this year, as the country is closer than ever to eradication," the organization said.

Pakistan is one of only three countries where the disease is endemic. The virus usually infects children living in unsanitary conditions, attacks the nerves and can kill or paralyze.

The government, teaming up with U.N. agencies, is on a nationwide campaign to give oral polio drops to 34 million children under the age of five. This is the third of four nation-wide anti-polio vaccination campaigns scheduled for this year in Pakistan, said Michael Coleman, a spokesman with UNICEF's polio campaign.

But vaccination programs, especially those with international links, have come under suspicion in the country since a Pakistani doctor ran a fake vaccination program to help the CIA track down Usama bin Laden.

While security concerns have long made it difficult to reach areas such as North and South Waziristan in Pakistan's tribal regions near the Afghan border, the Taliban threats in June were the first time that militants had actively campaigned against the vaccination programs.

As a result, vaccinations are not taking place in those areas during this campaign.