(CNN) -

The growing refugee crisis in northwestern Pakistan is fueling the danger of spreading the polio virus among the displaced population, the World Health Organization warned on Wednesday.

More than 450,000 Pakistanis have fled their homes in the past two weeks as the military tries to root out militants in the North Waziristan region near the border with Afghanistan.

But "this number could reach 600,000 as the military operation continues," federal minister for states and frontier regions, retired Lt. Gen. Abdul Qadri Baloch, said during a news conference on Pakistan State TV Wednesday.

That could mean an even bigger danger of spreading the disease as the number of refugees increases.

Rising polio risk

Polio rates are higher than average in North Waziristan due to a ban on anti-polio campaigns imposed by the Pakistani Taliban two years ago in response to U.S. drone strikes.

In June 2012, Taliban commander Hafiz Gul Bahadur released a statement that said vaccines "would be banned in North Waziristan until the drones strikes are stopped."

He added that drone strikes "are worse than polio."

Polio is a highly infectious viral disease that primarily affects young children. It can lead to paralysis and death. The virus is easily preventable through immunization, but there's no cure once it is contracted.

"The highest number of polio cases have been witnessed in North Waziristan," Pakistan WHO spokesperson Dr. Nima Saeed told reporters in Islamabad. "The mass migration of people from the vulnerable area has increased the risk of the polio virus spreading further."

Mass vaccination

The WHO is working to contain the threat by vaccinating people along routes out of North Waziristan.

Many are receiving the dose at government-run centers set up to register displaced people.

As of Wednesday, the U.N. said around 146,000 people had been vaccinated.

Hundreds of thousands of people have fled North Waziristan since the launch of a government offensive on June 15 against the Pakistani Taliban in the tribal areas bordering Afghanistan.

The United Nations says most of the people who have fled the region have sought shelter with relatives and in rented accommodation in the town of Bannu, in Bannu district.

One government-run camp has been set up by the government with enough room for 200,000 people, but so far only around 20 families have moved there.

"The facilities in the camp aren't yet up to the standard that we'd like them to be. Also, for cultural reasons people don't want to live in tents," said Timo Pakkala, the U.N's Humanitarian Coordinator for Pakistan.

"The people who come from North Waziristan are very conservative, very traditional. There are restrictions on men and women staying together. They have families; they want to stay together," he said.