Islamabad, Jan 21 (IANS): At least three people, including two women, were killed Tuesday and another injured when a polio team was attacked in Pakistan's Karachi city.

Police said the killing of the polio workers was a bid to terrorise and stop polio teams in the city so that they abandon the campaign which entered its second day Tuesday, Dawn online reported.

Police said four armed men riding bikes opened fire on the polio team in Qayyumabad area, injuring four workers. Of them, three succumbed to injuries on their way to hospital.

No group has claimed responsibility for the attack but militants have frequently targeted polio workers in the past.

The attack comes a day after authorities in Sindh began to inoculate 7.6 million children with polio vaccine as part of a nationwide drive that will continue until Thursday.

The children in Sindh are among 33 million Pakistani children who are being administered polio vaccine as part of the National Immunisation Day that was observed Jan 19 and extended to Jan 23.

Pakistan is one among the three countries in the world where polio is still endemic as efforts to stamp out the disease have been frustrated by terrorists.