An Afghan official has said fighters used a bomb and small arms to kill a representative of a government peace council entrusted with helping start talks with the Taliban.
Omaer Zawak, a spokesman for the governor of Helmand, said the attack that killed Malim Shah Wali Khan on Wednesday also wounded the province's deputy governor.
A bodyguard also died and four others were wounded.
He said the armed group first detonated a bomb next to Khan's car and then attacked with assault rifles.
A day earlier, at least 12 people, including three British soldier, were killed by a roadside bomb in Helmand.
Six British soldiers have now been killed this year in Afghanistan, where British casualties have slowed over the past year.
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In a statement, Major Richard Morgan, UK Ministry of Defence spokesman, said: "Security in Helmand, where most UK forces are based, is steadily improving, with Afghan forces already responsible for the bulk of the province - but the environment in which our troops operate remains risky and dangerous, including the threat of improvised explosive devices and insurgent attacks.
"We will continue to do all we can to minimise these risks but they can never be removed entirely."
Helmand, which is the largest producer of opium in Afghanistan, has been the scene of the some of the fiercest fighting between NATO-led foreign forces and their Afghan government allies and the Taliban.
Fear is mounting that Afghanistan could be engulfed in turmoil after the pullout of most NATO combat troops by the end of 2014.
A presidential election is also due that year.
NATO and its partners are training Afghanistan's 350,000-strong security forces, though questions remain over how well the Afghans will be able to tackle the insurgency.
Last week, the Taliban vowed to start a new campaign of suicide attacks on foreign military bases, diplomatic areas as part of their spring offensive against the US-backed government.