The explosion happened near the police chief`s compound in the provincial capital and appeared to target a joint Afghan police and army patrol.
The Ministry of Interior condemned the attack and in a statement described it as "un-Islamic and inhumane". It said the toll was 12 dead policemen and a child.
Twelve people were wounded in the blast, nine of them policemen and three civilians, said Daoud Ahmadi, spokesman for the Helmand provincial governor.
It comes after a string of destabilising assassinations of high-profile southern leaders, including President Hamid Karzai`s younger brother, and just days after suicide attackers with guns killed 19 people, most of them children.
Afghan forces took over security responsibilities in Lashkar Gah this month, the most contentious of the first seven areas for which foreign troops handed over duties.
The gradual transition of security control to Afghan forces is due to be completed by the end of 2014.
Helmand province has been the site of some of the most vicious fighting of the war. Far more foreign troops have died there than in any other province and there are still several Helmand districts dominated by the Taliban.
Violence in Afghanistan is at its worst since U.S.-backed Afghan forces toppled the Taliban government in late 2001, with high foreign troop deaths and record civilian casualties.
Roadside mines killed 17 civilians in Helmand province on Friday when a minibus and tractor separately struck explosives. (M014/K004)
Editor: Kunto Wibisono
Copyright © ANTARA 2011
