Afghanistan has begun its latest drive to vaccinate millions of children under five against the crippling polio virus, United Nations Assistance Mission in Afghanistan (UNAMA) officials have said.

The three-day campaign is the fifth in Afghanistan this year and was launched Sunday by the Afghan Ministry of Public Health (MoPH), with the support of the United Nations Children's Fund (UNICEF), the World Health Organization (WHO), Rotary International and other partners.

Afghanistan, one of just four countries in the world where polio is endemic, has seen the number of people suffering from the disease surge this year. There have been 29 confirmed polio cases in 2006, compared to only nine cases last year, according to the WHO in Kabul.

"This is a massive campaign and involves 34,000 volunteers administering drops of polio vaccine to 7.2 million children across the country," UNAMA spokesman Adrian Edwards said in Kabul.

Many new polio cases recorded this year have been in southern Afghanistan, which is experiencing a deadly phase of Taliban-led violence. Officials say the deteriorating security situation in the south, which has hampered polio immunisation drives, has been the leading cause of an increase in the disease in the impoverished country.

"One of the most important aims of the campaign is to curtail the polio virus in southern Afghanistan and minimise the risk of it spreading to other parts of the country," Dr Tahir Mir, medical officer for polio vaccination at the WHO, told IRIN.

During the September and August polio vaccination drives, about 75,000 children were missed out in the southern region and about 50,000 children were not immunised in the Karabagh, Nawa, and Gilan districts of southeastern province of Ghazni due to security problems, according to the WHO.

Unregulated travel to and from Pakistan, where polio still exists, difficulty in establishing health services, a lack of awareness and poor communication with community leaders were the main factors fuelling polio's spread in the impoverished Central Asian state, health officials said.

Polio is a highly infectious virus that invades the nervous system and can cause total paralysis in hours. It can strike at any age, but mainly affects children under five. It enters the human body through the mouth and multiplies in the intestine. Besides Afghanistan, polio remains endemic in Nigeria, India and Pakistan.