Karachi: Health workers on Sunday administered polio vaccines to thousands of children in 24 high risk areas in this southern city amid high security a day after a deadly attack polio workers in the north left 12 people dead.

The provincial government banned passengers from sitting pillion on motorcycles in 24 union councils (UCs) that were left out in the last round of vaccinations. The ban was imposed to prevent attacks on the polio workers.

In January, pillion motorcycle riders shot dead at least three workers, including two women, in the eastern part of the city. They were carrying out a door-to-door vaccination campaign.

Police and paramilitary rangers were assigned to protect the polio teams in the 24 UCs, which were sensitive both in terms of security and their vulnerability to the polio virus.

Syed Saidfur Rehaman, the deputy commissioner of the central district, said since schools were closed on Sunday almost all children were at home to get the vaccine.

The campaign aimed to vaccinate children up to five years of age in the 24 areas. The authorities also used the campaign to collect health information that signifies basic health indicators.

In the town of Jamroud, in northern Pakistan, 11 paramilitary soldiers and one child died when bombs detonated in the Lashora area of the town in Khyber Agency.

The soldiers were protecting a convoy of anti-polio campaigners.

Polio persists in Pakistan with militant groups seeing vaccination campaign as a cover for espionage. They people also fear that the polio drops cause infertility.

World Health Organisation described Pakistan as the only polio-endemic country where polio cases registered an increase in 2013 in comparison to 2012.