Two United States advisers who were shot dead in Afghanistan's interior ministry by an Afghan colleague had been mocking anti-US protests over the burning of the Koran, a government source said.
The description of the shooting - which led to NATO pulling all its advisers out of Afghan government ministries - came amid renewed violence in a sixth day of anti-American demonstrations.
A protester was killed and seven US soldiers were wounded in a grenade attack on their base as France, announced its Kabul embassy was temporarily withdrawing all its civilian mentors and advisors from Afghan institutions for "safety reasons".
Germany also said it had withdrawn its national and international staff from Afghan ministries as a "precautionary measure".
Describing the sequence of events that led to the interior ministry shootings, the source said the US advisers were "scolding the protesters and calling them bad names" as they watched videos of protests in Kabul.
"They called the Koran a bad book in the presence of (an Afghan colleague). After all this the guy had verbal arguments with the advisers and was threatened by them. He gets angry and shoots them. Eight rounds were fired at them," the source added, requesting anonymity.
"He then sneaks out and disappears. No-one knew about the incident for more than an hour because the room is soundproofed," he said, adding that CCTV cameras had been viewed in the investigation of the shooting.
Asked about this description of events in the ministry, a spokesman for NATO's US-led International Security Assistance Force said: "The investigation is ongoing."
Government sources said police were hunting for an Afghan intelligence official suspected of killing the two Americans, while the interior ministry confirmed that "the suspect is one of the employees of the ministry and he is at large".
Local television quoted a source which named the suspect as 25-year-old Abdul Saboor, who had studied in Pakistan and joined the ministry as a driver in 2007 before being promoted.
Sunday's grenade attack came during an anti-US protest in northern Kunduz province over the burning of Korans in an incinerator pit at the Bagram airbase, police said.
"The demonstrators hurled a hand grenade at a US special forces base in Imam Sahib town of Kunduz province. As a result seven US special forces were wounded," Kunduz police spokesman Sayed Sarwar Hussaini said.
A spokesman for NATO forces said: "According to initial reports, an explosion occurred outside of an ISAF installation in northern Afghanistan early this afternoon."
He said ISAF officials were "gathering details at this time".
Local officials said one person was killed in the anti-US demonstration in Imam Sahib as some 2,000 anti-US protesters tried to march on the provincial capital but were stopped by police.
"One dead and seven wounded protesters have been brought to hospital from Imam Sahib district so far," hospital official Mohammadullah said.
In the neighbouring province of Samangan, two protesters were wounded during a one-hour demonstration in Aybak city, provincial governor Khairullah Anosh said, but there were no reports of unrest elsewhere in Afghanistan.
The latest death brings the total toll in six days of demonstrations since the Koran burning to more than 30.
Appeal for calm
President Hamid Karzai went on television to appeal for calm.
Mr Karzai "condemned with the strongest words" the treatment of Islam's holy book and said the perpetrators should be punished, but told his countrymen: "Now that we have shown our feelings it is time to be calm and peaceful."
He said he respected the emotions of Afghans upset by the Koran burning, but urged them not to let "the enemies of Afghanistan misuse their feelings".
Taliban insurgents have called on Afghans to kill foreign troops in revenge for the incident, and claimed to have been behind the shooting deaths of the two US advisers in the interior ministry in Kabul.
NATO, which has a 130,000-strong US-led military force fighting the Taliban insurgency, has advisers throughout the Afghan government but commanding officer General John Allen ordered them all to be withdrawn.
"Despite being pulled from the ministries, the military advisers remained in contact with ministry personnel," ISAF spokesman Lt Col Jimmie Cummings said.
"We will not let this incident divide the coalition," he said on ISAF's Twitter feed.
But analysts said it had plunged relations between Afghans and their Western allies to an all time low.
"It has never been as bad as this and it could be a turning point" in the West's 10-year mission in the war-torn country, said Martine van Bijlert of the Afghanistan Analysts' Network.