Islamabad, Jun 10 (IANS): The World Health Organisation (WHO) has expressed concern over emergence of new polio cases in Pakistan's northwest tribal region, where around 150,000 children have reportedly not been immunized against the deadly virus.

At least eight cases have been detected in Khyber agency this year, one from Tirah and seven from Bara town, Dawn News reported.

Khyber agency is the only area in Asia having both the polio virus 1 and 3 types.

Zabia, the 23-month-old daughter of Noor Jan, a resident of Akakhel area of Tirah, has become the latest case recorded in the region.

Zabia did not receive any dose of the oral polio vaccine, as the area where she lives has not been visited by any medical team since September 2009 due to fear over terror attacks.

The WHO said spread of the virus will continue unabated as long as anti-polio programmes continue to miss a significant number of children, either due to insecurity or poor quality health campaigns.