Pakistan has seen a major fall in polio cases this year, officials said Thursday, as a military operation has allowed vaccinators to reach areas previously off-limits because of militant attacks.

The World Health Organization (WHO) said there had been 24 cases since January 1, a decline of over 70 percent from the same period last year, when there were 84 cases.

Pakistan is one of only three countries where polio remains endemic and last year saw 306 cases of the highly infectious, crippling disease -- a 14-year record.

Attempts to eradicate polio have been badly hit by opposition from militants, who say the programme is cover to spy on their operations. Their attacks on immunisation teams have claimed 78 lives since December 2012.

Elias Durry, WHO's senior coordinator for polio eradication in Pakistan, confirmed the drop in cases, saying intensive vaccination efforts were paying off.

"Compared to last year, this year polio cases in Pakistan have been 70 percent decreased," Durry told AFP.

"In 2013 and 2014 the programme was under pressure, but in 2015 the virus is under pressure."

Rana Muhammad Safdar, a senior official at the Pakistan National Institute of Health, confirmed the WHO data.

The government "declared war" on polio in November after the 14-year record was breached and in the wake of a damning international report that slammed the country's campaign to tackle the virus as a "disaster".

Durry said the main reason for the fall in cases was better access to families in previously unvaccinated areas, where troops have been advancing.

"The accessibility of children in places that were not being access before... is the number one reason, including proper implementation of the plan," he said.

Pakistan's military in June last year launched a ground and air blitz against militant groups in the North Waziristan tribal area, forcing millions of civilians to leave their homes and settle in other districts.

All those fleeing North Waziristan were given polio drops as they entered neighbouring Khyber-Pakhtunkhwa province, allowing health workers a chance to reach families who had not been vaccinated for years.

The Taliban had imposed a blanket ban on polio vaccination in the areas it controlled in North Waziristan, saying the health initiative was cover for spying.

Durry said health workers had also vaccinated children in Pakistan's largest city, Karachi.

"The thing is not only accessing Waziristan but also accessing children in places like Karachi and other places.....(and it is) because of working with the community," Durry said.