KABUL (AFP) - A bomb exploded outside an Afghan police headquarters Sunday, killing four civilians including two children, officials said, also reporting a dozen militants were killed in a joint US-Afghan operation. Separately, the Afghan defence ministry confirmed that 19 militants killed on Friday and Saturday were linked to an attack on an outpost in remote northeastern Kunar province that left 10 dead, including US and Latvian troops. The insurgent Taliban movement claimed responsibility for Sundays bomb blast in the southern province of Helmand, a militant hotspot that is hit by regular attacks. The explosives were placed on a motorcycle in Gereshk district, Helmand govt spokesman Daud Ahmadi told AFP. Four civilians were killed. Two children were among the dead, Ahmadi said, adding that seven others, including two policemen, were wounded. The interior ministry said in a statement that only three civilians were killed, including an eight-year-old girl and a 10-year-old boy. Eight were wounded, one of them a policeman, it said, adding the blast was outside the district police headquarters. The interior ministry said separately that a two-day sweep of the southern province of Uruzgan and involving 200 policemen working with US-led coalition troops had ended on Saturday. Twelve armed terrorists including three commanders were killed, it said in a statement. Bombings, including suicide attacks, are among the main tactics that the Taliban use to target Afghan and international forces as part of an Al-Qaeda-backed insurgency, although civilians are most often harmed. The Taliban, who were in government between 1996 and 2001, warned last week they would step up ambushes, suicide attacks and bombings in a new operation. In the most severe attack on international forces in months, three US soldiers and two Latvian troops were killed on Friday when their base was stormed by militants in mountainous Kunar. Four Afghan soldiers and an interpreter also died in the attack in the district of Ghaziabad.