ministry in Kabul on Saturday in an attack blamed on a rogue Afghan intelligence official and claimed by the Taliban as a response to the Koran burning.
Afghan demonstrators clash with policemen during a protest against Koran desecration in Kabul. AFP/Shah Marai
The toll since the incident at Bagram airbase north of Kabul, which inflamed anti-Western sentiment already smouldering in Afghanistan over abuses by US-led foreign troops, rose on Sunday to more than 30.
In the sixth day of demonstrations, one protester was killed and seven US soldiers were wounded in a grenade attack on their base.
The Pentagon said on Sunday that Afghanistan's defense and interior ministers had cancelled a visit to Washington this week to concentrate on addressing security concerns at home.
US defense secretary Leon Panetta "understands why that's a priority and why they are unable to travel to Washington in the coming days", Pentagon spokesman George Little said in a statement.
US officials have apologised repeatedly for the burning of the Korans, which they said were inadvertently sent to an incinerator pit at the airbase.
Nato has pulled all its advisers out of Afghan government ministries and France announced on Sunday its Kabul embassy was temporarily withdrawing its civilian mentors and advisers from Afghan institutions for "safety reasons".
Germany also said it had withdrawn its national and international staff from Afghan ministries as a "precautionary measure".
An Afghan government source said the two US advisers killed at the interior ministry had been mocking anti-US protests over the burning of the Koran.
Describing the sequence of events that led to the shootings, the source said the pair were "scolding the protesters and calling them bad names", as they watched videos of the demonstrations 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 on Saturday, 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.
Police said Sunday's grenade attack came during an anti-US protest in northern Kunduz province over the Koran burning.
"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 told AFP.
President Hamid Karzai went on television Sunday to appeal for calm.
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.
Analysts said that relations between Afghans and their Western allies have plunged 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.