A suicide bomber on a motorbike blew himself up in a bazaar in southern Afghanistan on Sunday, killing 24 people and wounding more than two dozen others, police said.
The blast came as international and Afghan security forces battled militants on several fronts, with the US-led coalition announcing it had killed at least 40 insurgents in an ongoing operation in the volatile south.
The clashes come amid a surge in the insurgency-linked violence wracking Afghanistan, including a suicide bomb in Kabul last week that left 41 civilians dead and US-led air strikes early this month that officials said killed 64.
On Sunday, a suicide attacker with bombs strapped to his body rammed a motorbike into a police vehicle in a bazaar in Uruzgan province, causing an explosion that ripped through several shops, a witness said.
Twenty civilians and four policemen were killed in the blast in Deh Rawood, 400 kilometres (250 miles) southwest of Kabul, said Uruzgan police chief Juma Gul Hemat, adding that 27 wounded people were being treated in hospital.
"Most of the casualties are shopkeepers and people and children who were selling stuff on the roadside," said a shopkeeper who gave his name only as Fazlullah.
"Around 15 shops have been damaged. I saw lots of people killed and injured. I can see human flesh, blood and pieces of metal, wood, clothing scattered around. Everything is bloodied," he told AFP by telephone.
There was no immediate claim of responsibility for the bombing, but similar attacks have been carried out by Taliban militants, who have led an insurgency against the Kabul government since being ousted from power in late 2001.
President Hamid Karzai condemned the attack, blaming the "enemies of Afghanistan" -- a reference to Taliban and other insurgents.
The US-led coalition, helping Afghanistan fight the extremists, meanwhile announced that it had killed at least 40 militants in an operation still under way in the southern province of Helmand.
The fighting started on Saturday after militants ambushed an Afghan and international security patrol in the province's volatile Sangin district, it said in a statement.
"The ensuing fight led ANSF (Afghanistan National Security Forces) and coalition forces to return fire and call for precision air strikes," it said.
"At least 40 militants have been killed in the last two days, while over 30 enemy boats and several ... bridges were also destroyed on the Helmand River." A soldier with the same unit was killed by a bomb blast Sunday, the coalition announced earlier.
In the northeast, NATO-led and Afghan soldiers were engaged in heavy battles in Kunar province, after an outpost came under attack early Sunday, officials said.
"The fighting started early today and it's still ongoing. We have taken casualties," said Captain Mike Finney, a spokesman for the NATO-led International Security Assistance Force.
He could not immediately give details.
Four Afghan soldiers had been wounded, defence ministry spokesman Mohammad Zahir Azimi told AFP. "Tens of enemies have been killed and wounded but we don't have a figure," he said.
The troops had responded with air strikes, the deputy provincial governor of adjoining Nuristan province, Abdul Aleem, told AFP.
"Some homes were destroyed and damaged. There have been casualties among all three sides -- the locals, Taliban and foreign forces," he said.
Also in Nuristan, four police were missing after days of clashes with insurgents in a district on the border with Pakistan, Aleem said.
Insurgents had overrun two police posts in Bargi Matal district, he said. Two of the insurgents were also killed, Aleem said.