Development marks attitude change of militants, who previously allowed medics into region but now suspect them of spying

The Taliban has banned polio vaccination teams from southern Helmand because it suspects them of spying for the government at a time of heavy clashes with government forces, the insurgent group said in a statement on its website.

The announcement is a worrying development, because although Taliban groups across the border in Pakistan have attacked and killed polio vaccinators for years, their Afghan counterparts have mostly supported, or at least tolerated, international efforts to wipe out the disease.

The last time polio vaccinators were blocked from part of Afghanistan, the insurgent group denied any role and said it supported efforts to stop the disease.

Afghanistan is one of just three countries, along with Pakistan and Nigeria, where polio is still endemic. There has been a rise in cases this year, with seven reported so far compared with just three for the same period of 2013, according to the Global Polio Eradication Initiative.

The group said Helmand has been off limits to vaccinators since February, but did not give a reason. The southern province has seen fierce fighting between insurgent and government forces in recent weeks, and the Taliban's statement was the first indication it had chased out polio eradication teams.

"We have stopped vaccination in Helmand for the moment," the Taliban said in a statement posted on its website this week. "The vaccinators were also collecting information about the Taliban and Taliban commanders, they were spying."

The statement said they had asked UN officials for talks but received no response; the UN's humanitarian arm declined to comment when asked about the ban.

Health workers often negotiate access to difficult areas through village elders, and most Afghans are keen to protect their children from a disease which can kill or paralyse. The Taliban's accusation that vaccinators were working as spies is a worrying new sign of hostility to efforts to wipe out the disease.

But there have for years been fears that the Pakistani Taliban's opposition to polio vaccination campaigns, which militant leaders have banned at least three times since 2012, could influence Afghan groups.

The CIA's decision to set up a fake vaccination programme as part of its hunt for Osama bin Laden fuelled militant suspicion of the global project to eradicate polio. The White House has since promised that the US will never again use vaccination programmes as a cover for spying.

Most polio cases in Afghanistan are believed to be the result of infections brought across the Pakistani border, but Afghans are still vulnerable because in some areas only two-thirds of children are immunised.