In an entirely separate but similar incident, another Nato soldier died and a second was seriously wounded by a roadside bomb.
British and Canadian troops make up the majority of the alliance's International Security Assistance Force (Isaf) in Helmand and neighbouring Kandahar provinces.
However, there is no indication of the dead soldiers' nationality so far.
More than 5,000 Nato troops are currently engaging in an offensive to blunt the Taliban, who continue to offer resistance in Afghanistan's southern provinces six years after being ousted by a US-led coalition.
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