Four people have been killed in the Afghan city of Kandahar during a demonstration against the burning of a Koran in the US.
It followed a protest over the same issue in the northern city of Mazar-i Sharif on Friday left 14 people dead, including seven UN workers.
It was the worst attack on the UN mission in Afghanistan since the international invasion in 2001.
Separately, three insurgents were killed when they attacked a Nato base.
They were stopped before they could enter the compound, Nato and Afghan police said.
At least one was wearing a burqa, news agencies reported on Saturday, quoting police sources.
Hundreds of people joined the demonstrations in Kandahar on Saturday. Gunfire was heard in Kandahar and plumes of smoke rose from cars that had been set on fire.
Hospital officials told the BBC 15 people had been injured. A BBC correspondent in Kandahar says the city is under lockdown.
UN Secretary General Ban Ki-moon condemned the violence in Mazar-i Sharif as "outrageous and cowardly". Afghan President Hamid Karzai said it was inhumane and against Islamic and Afghan values.
The Taliban has denied it carried out the attack.
"The Taliban had nothing to do with this, it was a pure act of responsible Muslims," spokesman Zabihullah Mujahid told the Reuters news agency by phone from an undisclosed location.
"The foreigners brought the wrath of the Afghans on themselves by burning the Koran," he said.
Local police told the BBC that 27 people had been arrested following the demonstration in Mazar-i Sharif.
The demonstrators were angered by the actions of US Pastor Wayne Sapp, who set light to a copy of the Koran at a church in Florida on 20 March.
The burning took place under the supervision of Pastor Jones, who last year drew condemnation over his aborted plan to burn copies of the Koran on the anniversary of the 9/11 attacks.
Pastor Jones has denied responsibility for the lethal protests in Afghanistan.
Witnesses said the protest began peacefully but suddenly turned violent.