Allauddin Khan / AP

An Afghan villager, right, shows an empty canister allegedly used by US forces during Sunday's killing of civilians at a prayer ceremony for victims in Panjwai, Kandahar province, on March. 13, 2012.

Allauddin Khan / AP

Villagers listen to speeches during a prayer ceremony for victims of Sunday's killing, in Panjwai on March. 13, 2012.

Allauddin Khan / AP

Afghan security forces take up positions in a dried water canal after Taliban militants opened fire on a delegation of senior Afghan officials in Panjwai on March. 13, 2012.

Suspected insurgents opened fire on Tuesday on senior Afghan investigators of the massacre of 16 civilians by a lone U.S. soldier, Afghan officials said, just hours after the Taliban threatened to behead American troops to avenge the killings.

The gunmen shot from long range at two of President Hamid Karzai's brothers, Shah Wali Karzai and Abdul Qayum Karzai, and security officials at the site of the massacre in Kandahar's Panjwai district.

Karzai's brothers were unharmed in the brief battle, which began during meetings with local people at a mosque near Najiban and Alekozai villages, but a soldier was killed and a civilian wounded. 

In Washington, President Obama said he viewed the killing of 16 Afghan civilians as seriously as if those killed had been Americans.

"The U.S. takes this as seriously as if it were our own citizens and our own children who were murdered," Obama said at the White House.

-- Msnbc.com and news services contributed to this post

Slideshow: Afghanistan: Nation at a crossroads

Jangir / AFP - Getty Images

More than ten years after the beginning of the war, Afghanistan faces external pressure to reform as well as ongoing internal conflicts.

Launch slideshow

Marko Djurica / Reuters

Women mourn in front of coffins prepared for a mass burial at the Memorial Center in Potocari, near Srebenica July 10. The bodies of 614 recently identified victims of the Srebrenica massacre will be buried on July 11, the anniversary of the massacre when Bosnian Serb forces commanded by Ratko Mladic slaughtered 8,000 Muslim men and boys and buried them in mass graves, in Europe's worst massacre since World War II.

 Read one mother's story here.

Dado Ruvic / Reuters

A forensic expert from the International Commission for Missing Persons (ICMP) works on trying to identify the remains of a victim of the Srebrenica massacre, at the ICMP centre near Tuzla, Bosnia on June 1.

The painstaking task of identifying the victims of the Srebrenica massacre continued today, almost 16 years after 8,000 Muslim men and boys were killed in the Bosnian town. The work is carried out by the International Commission on Missing Persons, an organization established to support the Dayton Peace Agreement that ended the 1992-95 war in Bosnia.

Former Bosnian Serb General Ratko Mladic was handed over to U.N. officials in the Hague yesterday after being extradited from Serbia. Mladic faces charges of genocide and other war crimes for atrocities committed by soldiers under his command, including the events of July 1995 in Srebrenica. Read the indictment (link opens a PDF document).

Related content:

• Mladic extradited to UN court in The Hague
• Muslim boy in Srebrenica video with Mladic looks back
• Video - Srebrenica welcomes Mladic arrest: