The attack happened yesterday on the eastern outskirts of provincial capital Quetta when a team of seven polio workers was getting ready to launch the fourth and final day of the campaign when two men riding a motorbike opened fire on their vehicle, killing four.
A health official from Quetta said that the World Health Organisation has suspended its operations in Balochistan due to security threats to polio workers.
Unicef has also scaled down its activities in Baluchistan due to security threats to its staff, another official said.
The WHO and the United Nations International Children's Educational Fund have been assisting the provincial government of Baluchistan in eradicating polio virus from the province for more than twenty years.
After the yesterday's deadly attack, polio vaccinators refused to go back to work unless they are assured of greater security.
Meanwhile, Chief minister Abdul Malik Baloch ordered a probe into the attack.
Inspector General Police Balochistan, Amlaish Khan has suspended Deputy Superintendent of Police Shafqat Amer and an SHO for their failure to prevent the attack.
A polio vaccination campaign was launched earlier this month amid tight security in 11 districts of Balochistan, Pakistan's largest but least developed and most sparsely populated province.
Pakistan government has come under criticism for doing little to eradicate the virus.
Polio is still endemic in Pakistan, Afghanistan and Nigeria.
The number of polio cases recorded in Pakistan has reached 246 for the year -- a 14-year high and more than double the total for the whole of 2013.
