The attack happened in the Nehre Siraj district of southern Helmand province, the local police chief told the BBC.
There have been several recent poisoning incidents involving members of the Afghan National Police, the BBC’s Bilal Sarwary reports from Kabul.
It comes amid attempts by the Taliban to infiltrate the security forces.
Three police officers have been reported missing – along with their weapons and a police vehicle – following Tuesday’s attack in Helmand.
They are believed to have been working with the Taliban, intelligence officials told our correspondent.
Helmand’s police chief Ahmad Nabi Ilham said the Taliban militants had first poisoned the police officers’ yoghurt before launching a full scale attack on the checkpoint.
Similar tactics had been used by insurgents in Helmand before, Dawood Ahmadi, spokesman for the provincial governor, said.