Militants in Afghanistan on Tuesday attacked a government delegation -- including two of President Hamid Karzai's brothers -- visiting the site where a U.S. soldier killed 16 civilians over the weekend, news reports said.

Several top security officials were also in the delegation in Panjwai in southern Afghanistan's Kandahar province, the BBC reported.

One Afghan soldier and three militants were killed, police said, and the delegation headed back to Kandahar.

The attack came as about 600 students in the eastern city of Jalalabad staged the first major protest in response to Sunday's shootings, raising worries of a repeat of the wave of violent demonstrations that rocked Afghanistan after what Americans said was the inadvertent burning of Qurans at a U.S. base.

The protesters in Jalalabad condemned the Kandahar attack, chanting, Death to America! Death to Obama!

On Tuesday, militants killed an Afghan soldier who was providing security for the delegation in the village of Balandi, said Gen. Abdul Razaq, police chief for Kandahar province. Another Afghan soldier and a military prosecutor were wounded, he said.

The gunfire erupted as the delegation was in a mosque for a memorial service for those killed Sunday.

One of the president's brothers, Qayum Karzai, said the attack didn't seem serious to him, according to the Associated Press.

We were giving them our condolences, then we heard two very, very light shots, he was quoted as saying. Then we assumed that it was the national army that started to fire in the air.

Qayum Karzai said the members of the delegation, which also included Kandahar Governor Tooryalai Wesa and Minister of Border and Tribal Affairs Asadullah Khalid, were safe and headed back to Kandahar city.

Before Tuesday's attack, the Taliban vowed to kill and behead those responsible for the civilian deaths in the two villages in Panjwai district, considered the birthplace of the militant group.

The American soldier said to have carried out Sunday's attacks is under arrest, according to U.S. officials, though they haven't released his name. The 38-year-old Army staff sergeant is being held at an undisclosed location.

U.S. President Barack Obama has described Sunday's shooting as absolutely heartbreaking and tragic. But he said international forces must be withdrawn from Afghanistan in a responsible way, and would not rush for the exits, the BBC noted.

U.S. Defense Secretary Leon Panetta said Monday that the soldier in question could face the death penalty if found guilty.