A Taliban suicide bomber rammed an explosives-laden car into a NATO convoy close to the US embassy in Kabul on Tuesday, killing three soldiers and wounding at least 13 Afghan civilians.
At the side of the road, US and Polish troops gave first-aid to blood-stained comrades beside the wrecked remains of a military vehicle, but the nationality of the dead soldiers was not confirmed.
The massive blast occurred at about 8:00 am (0330 GMT) during heavy rush-hour traffic outside the Supreme Court and on a main road leading to the heavily-fortified US embassy.
"We can confirm three International Security Assistance Force (ISAF) members died as a result of an enemy attack in Kabul today (Tuesday)," the NATO coalition said in a statement.
"It is ISAF policy to defer casualty identification procedures to the relevant national authorities."
The blast shook nearby buildings as emergency vehicles raced through the streets to the scene on a main road that NATO convoys use every day.
"It was a suicide car bomber," Kabul police spokesman Hashmat Stanakzai told AFP.
"Our initial reports show 13 civilians were wounded and 17 civilian cars were damaged."Some civilians were treated on the scene, and some were taken to the hospital."
Video: Car bomb kills NATO troops in Kabul
The NATO force has now 41,000 troops in Afghanistan, with about 29,000 from the US and just 300 from Poland.
All NATO combat soldiers will withdraw by December after 13 years of fighting the Taliban, with a follow-on mission of about 12,000 troops likely to stay on into 2015 on training and support duties.
The Taliban quickly claimed responsibility for the attack via a recognised Twitter account.
"(A) powerful explosion destroyed 1 military vehicle, killing/wounding a number of American terrorists," said Taliban spokesman Abdulqahar Balkhi.
Taliban exploit election?
Afghanistan is stuck in a political stalemate over election results, with the two presidential candidates in talks to resolve the prolonged dispute over who won the June 14 vote to replace President Hamid Karzai.
Ashraf Ghani and Abdullah Abdullah have been wrangling over a power-sharing deal after the vote was engulfed in allegations of fraud that have threatened to spark instability as NATO troops pull out.
Ghani, who is widely tipped to emerge as the new president, won the run-off election according to preliminary results, but Abdullah has consistently said he was the victim of state-backed ballot-rigging.
Both campaign teams have previously said the deal hinges on the power held by a new chief executive officer, who would be nominated by the election loser.
The stand-off has threatened to wreck hopes that the US-led military and civilian aid effort since the fall of the Taliban regime in 2001 would leave Afghanistan as a democratic country.
With the government paralysed for months, it has also emboldened the Taliban insurgents, weakened the fragile economy and put future international military and aid support at risk.
The United Nations has expressed fears that a disputed election result could revive the ethnic violence of the 1990s civil war, when nationwide chaos allowed the Taliban to come to power.
It was the first major attack for weeks in Kabul, which has been regularly hit by complex Taliban attacks on the airport, luxury hotels, restaurants and foreign compounds.
In August, four civilians were killed in a similar attack on a NATO convoy in Kabul. No soldiers died in that blast, which wounded at least 35 bystanders.
Separately, ISAF said one coalition soldier was shot dead on Monday by a man wearing an Afghan National Army uniform.
So-called "insider attacks" have undermined relations between foreign soldiers and the Afghan military, which is being trained to take on the Taliban alone after NATO's exit.