Nine international soldiers and three Afghan civilians were killed in a bloody weekend of attacks in Afghanistan linked to a Taliban-led insurgency, officials said.
The attacks came amid growing concern about extremist violence in the war-torn country and across the border in Pakistan, more than seven years after the Taliban were removed from government in a US-led invasion.
The Taliban claimed responsibility for a blast that killed four International Security Assistance Force troopers in the eastern province of Nangarhar on Sunday, on the border with Pakistan.
"It was an IED (improvised-explosive device). Four soldiers were killed," an ISAF spokesman at the force's Kabul headquarters told AFP.
A statement said that two were killed immediately and two died later from their wounds.
The US military said the four were from the United States, which has about 38,000 soldiers in Afghanistan.
An Afghan media officer in the province said the bomb had been remotely detonated to hit a convoy in Bati Kot district.
"These dedicated professionals have risked their lives for a safe and stable Afghanistan," ISAF spokesman Brigadier General Richard Blanchette said.
Two British soldiers from the Royal Electrical and Mechanical Engineers were killed in an explosion while on vehicle patrol on Sunday in the Garmsir district in southern Helmand province, the Ministry of Defence in London said.
Three other ISAF soldiers died in Afghanistan on Saturday. One was French, another British and the nationality of the third has not been released.
With Sunday's strikes, 63 international soldiers have lost their lives in Afghanistan this year, most of them in insurgent attacks, according to a toll by the icasualties.org website that tracks the wars here and in Iraq.
Also on Sunday, a suicide bomber blew up an explosives-laden vehicle in the capital Kabul as a foreign military convoy passed, the interior ministry said.
The blast left two civilians dead and 14 wounded, although the foreign troops were unharmed, it said.
Earlier, a bomb exploded in the southern city of Kandahar as the mayor, Ghulam Haidar Hameedi, drove past, police said.
"One civilian was killed and six others were wounded but there was no harm to the mayor except his vehicle was damaged a bit," police said.
The Taliban, who were in government between 1996 and 2001, have carried out a wave of similar attacks across the besieged country with other radical factions and criminals also behind a tide of violence.
The US military said meanwhile that soldiers killed five militants in an operation early on Sunday about 60 kilometres (40 miles) west of Kandahar city.
Three others were detained, it said in a statement.
ISAF has swollen to reach nearly 62,000 soldiers from 42 countries, according to its website. The separate US-led coalition is believed to include around 13,000 troops.
Another 17,000 US troops are expected to start deploying to the south in the coming months.
But with attacks at a record high last year, there has been increasing talk of finding a non-military way out of the spiralling violence, with Washington raising the possibility of peace talks with "moderate" Taliban.
The insurgents insist however they will only enter negotiations after the departure of the foreign troops propping up the Western-backed Afghan government.
Abdul Qayoum Karzai, a brother of President Hamid Karzai, who leads reconciliation efforts on behalf of Kabul, said US President Barack Obama's comments about exploring talks had sparked optimism, including amongst Taliban.
"No other way is left but talks," Karzai added. He would not give details about the process citing its sensitivity.