A suicide attack in south Afghanistan has killed at least 21 people, many of them children, police say.
The bomb was detonated in a market in the Deh Rawud district of Uruzgan province at about 1030 local time.
Provincial police chief Jumma Gul told the BBC that a suicide bomber on a motorbike had struck a police vehicle.
Militants in Kunar province attacked a Nato outpost, leading to clashes and casualties on both sides, said a statement by the alliance.
It said insurgents had been using shops and the mosque in the village of Wanat for cover.
"There have been casualties on both sides of the fight, but accurate numbers could not be confirmed as the fighting is ongoing," the announcement by the International Security Assistance Force (Isaf) said.
And US forces said 40 insurgents had been killed in Helmand province in the past 24 hours.
There is no confirmation.
A local official, quoted by Reuters, blamed Taleban fighters for the latest attack.
Officials said four of those killed in the Uruzgan attack were policemen and the rest were civilians.
A further 43 people were wounded.
Several shops were reported to have been destroyed by the blast.
The attack came as Nato-led and Afghan troops were engaged in fierce fighting with insurgents in the eastern Kunar province.
Insurgents were reported to have attacked a remote International Security Assistance Force (Isaf) outpost.
There is concern over the number of civilian deaths in Afghanistan
A local shopkeeper told AFP that the marketplace in Uruzgan was crowded when the bomb went off.
"Most of the casualties are shopkeepers and people and children who were selling stuff on the roadside," said the man, who gave his name as Fazlullah.
"I can see human flesh, blood and pieces of metal, wood, clothing scattered around. Everything is bloodied."
The BBC's Martin Patience in Kabul says no group has yet claimed responsibility for the blast but the Taleban are known to be active in the area.
Local government officials have been attacked by the Taleban in the past.
Some analysts believe that the movement has gained strength as it increases its attacks across Afghanistan.
Aid agencies have expressed concern about the rising civilian death toll in Afghanistan.
The Red Cross said that in July at least 250 civilians were killed or wounded over a six-day period.
The UN said recently that the number of civilians killed in fighting in the country had jumped by nearly two-thirds compared to last year.
On Monday a suicide bombing in Kabul killed more than 40 people.
The Afghan authorities are also investigating a US air strike in Nangarhar province last Sunday, in which 47 people died.