Suicide bombers have struck in three different parts of Afghanistan, killing at least 17 people, officials say.
The suicide bomb in Kabul killed at least three
The first bomb targeted Nato troops in Kandahar province. Four Canadian troops were killed and about 25 civilians - many of them children - injured.
Later in the capital, Kabul, a man in a car blew himself up as policemen approached, killing three.
In Herat, in western Afghanistan, a third bomber on a motorcycle killed at least 10 people and injured 18.
The BBC's Alistair Leithead in Kabul says the insurgency in Afghanistan continues to deepen, and the pressure on the international community increases.
News of the latest attacks came as Afghan troops launched a new operation in western Afghanistan, supported by the Nato-led International Security Assistance Force (Isaf).
On Friday Taleban rebels briefly captured a district headquarters in the western province of Farah, raising fears of a new front.
The violence had until now been fiercest in the south and east of the country.
The attack on Nato troops occurred when the bomber took a bicycle laden with explosives into a crowd of troops and children in Panjwayi district, about 25km (15 miles) west of the southern city of Kandahar.
"The soldiers were conducting a patrol in the area to provide security in supporting the Afghan security forces," said Brig Gen David Fraser, who commands Canadian Nato forces in southern Afghanistan.
One bystander described a horrific scene after the explosion.
"Kids were running towards the Canadian convoy because they were giving out pens and notebooks to the children," Mohammed Karim told the AFP news agency.
"A man riding on a bicycle approached the crowd and detonated in the crowd.
The Taleban said it carried out the attack. A spokesman, Qari Mohammad Yousuf, said the bomber was a young Afghan from Kandahar and promised more attacks.
Thirty-six Canadian soldiers and one diplomat have been killed since Canada became involved in Afghanistan in 2002.
On Sunday Nato said that at least 400 Taleban fighters had been killed in a two-week operation codenamed Medusa, the biggest offensive since Nato took over southern Afghanistan from US-led forces at the end of July.
The deaths cannot be independently verified.