"The suicide bomber detonated his auto bomb as spectators were leaving the stadium", Zwak said.
Aminullah Abed, the chief of the province's public health department, in Helmand province said the 12 killed and 40 wounded were received at a hospital in Lashkar Gha on Friday.
At least 12 people have been killed and dozens wounded in a vehicle bomb explosion near a sports facility in southern Afghanistan, a health official has said.
The explosion occurred after celebrations of Nowruz, the Persian new year, were winding down and revelers were on their way home, he added.
The police spokesman confirmed the blast was caused by a auto bomb.
Omar Zwak, a spokesman for the provincial governor, said the driver of the auto detonated his bomb after he was prevented from entering the venue. "The enemy has been beaten up badly by our fearless security forces across Helmand Province, and now they are trying to take revenge on civilians", he said. "We heard a loud explosion from our surgical centre in the city", Emergency tweeted.
"35 wounded already taken to our hospital, another four were dead on arrival", the NGO said in a Twitter post.
The office of Afghan president Ashraf Ghani issued a statement condemning the "brutal terrorist attack".
The attack caps a bloody few days in Afghanistan as Taliban and Islamic State militants ramp up attacks even before the official start of the spring fighting season.
KABUL-A sticky bomb detonated in the Afghan capital Kabul killing one person and wounding 13 others, officials said Saturday.
Over the same period, the watchdog said, the number of districts under Afghan government control or influence fell to its lowest level since December 2015.