Defence chief Leon Panetta says execution could be considered in case of soldier accused of killing 16 Afghan villagers.
Gunmen have attacked a senior Afghan government delegation investigating the massacre of 16 civilians by a US soldier in southern Kandahar province.
At least one Afghan soldier was killed as the delegation, which included two brothers of Afghan President Hamid Karzai, came under fire on Tuesday, Abdul Raziq, the police chief for Kandahar province, told the AFP news agency.
“There was an armed attack on them from a distance and the firing continued for about 10 minutes,” said a local reporter at the scene in Panjwayi district.
“Bullets were coming like rain on us,” another witness told AFP.
The attack came as hundreds of students took to the streets of the eastern city of Jalalabad, as anger over Sunday’s killings by the unnamed US soldier prompted more anti-US protests.
About 400 university students shouted “Death to America – Death to Obama”, burning an effigy of the US president and blocking the main highway to Kabul before dispersing after about two hours.
Amid the public anger, Barack Obama, the US president, once again pledged a full investigation.
“The United States takes this as seriously as if it was our own citizens or children. We are heartbroken at loss of innocent lives,” he said on Tuesday.
“I can assure the American people and the Afghan people that we will follow that facts wherever they lead us.”
Leon Panetta, the US defence secretary, told reporters a day earlier that the shooting suspect would be brought to justice under the US military legal code, and could face the death penalty if convicted.
Asked if the suspect could be sentenced to death, Panetta said: “My understanding is in these instances that could be a consideration.”
The Afghan Taliban threatened on Tuesday to behead US troops in revenge for the killings by the US soldier.
“The Islamic Emirate once again warns the American animals that the mujahideen will avenge them, and with the help of God will kill and behead your sadistic murderous soldiers,” Taliban spokesperson Zabihullah Mujahid said in an emailed statement.
Though the killings have outraged Afghans, they have not yet triggered a similar scale of protests that the burning of copies of the Quran at a US base sparked last month.
Abdul Rahim Ayoubi, a member of the Afghan parliament from Kandahar, told Al Jazeera that many locals were still deciding how to respond to the attacks.
“And once they decide, there will be no army, no force that can stop them,” Ayoubi said.
The US embassy in Kabul has warned its citizens to be on their guard, mindful of the prevailing mood in the country.