Islamabad, Sep 29 (IANS): A four-day polio campaign started in Pakistan Monday with an aim to inoculate children against the disease.

The campaign will be carried out across the country except for west Karachi, where a six-day campaign was launched Saturday, Dawn online reported.

Stringent security measures have been taken for volatile areas, particularly border areas between Sindh and Balochistan, where polio workers and doctors have been attacked previously.

A polio campaign had abruptly ended in Karachi once due to a World Health Organization (WHO) doctor being attacked. There have been numerous instances of such incidents over the years.

On Jan 21, three polio workers, two of them female, were killed in Qayyumabad in Sinsh province.

Health officials have refused to travel to Karachi on account of these events.

According to WHO, the total number of polio cases in Pakistan has escalated to 174 and the count is going up.

Fifty-eight cases were reported in 2012 and 93 in 2013.

Pakistan stands at the top of the last three polio endemic countries in the world - the other two being Nigeria and Afghanistan.