| CAMP LEATHERNECK, Afghanistan
CAMP LEATHERNECK, Afghanistan U.S. Defense Secretary Leon Panetta arrived in Afghanistan on an unannounced visit on Wednesday, as the United States tried to contain fallout from a massacre of 16 Afghan civilians by an American soldier.
A motorcycle bomb went off in Kandahar city in southern Afghanistan, killing an Afghan intelligence soldier and wounding two, as well as a civilian, while a roadside bomb killed 8 civilians in neighbouring Helmand province, officials said, as Panetta kicked off a two-day trip by visiting troops.
Panetta told them the weekend killings by what U.S. and Afghan officials have said was a lone rogue soldier would not undermine relations with Afghanistan.
"As tragic as these acts of violence have been, they do not define the relationship between the coalition and Afghan forces, and the Afghan people," he told soldiers at Camp Leatherneck, the main Marine base in the volatile southern province.
"We will be tested, we will be challenged. We'll be challenged by our enemy, we'll be challenged by ourselves, we'll be challenged by the hell of war," Panetta said.
Panetta's trip had been scheduled before Sunday's shootings in two villages in Kandahar province, but gained added urgency as political pressure mounted on Afghan and U.S. officials over the unpopular war, now in its eleventh year.
American soldiers are the likely targets of any backlash over the killings of villagers, who included nine children and three women, by a lone American soldier. The Afghan Taliban threatened to retaliate by beheading U.S. personnel.
But Panetta, the most senior U.S. official to visit Afghanistan since the shootings, said the massacre would not alter U.S. withdrawal plans and strategy.
Afghans investigating the incident had been shown video of the soldier, said to be a U.S. Army staff sergeant, taken from a security camera mounted on a blimp above his base, an Afghan security official who could not be identified told Reuters.
The footage showed the uniformed soldier with his weapon covered by a cloth, approaching the gates of the Belandai special forces base and throwing his arms up in surrender, the official said.
The video had been shown to investigators to help dispel a widely held belief among Afghans, including many members of parliament, that more than one soldier must have been involved because of the high death toll, the official said.
Panetta was to hold talks with Afghan leaders including President Hamid Karzai as tension remains high following a spate of incidents including the burning of Korans at the main NATO base in the country last month.
Panetta's arrival in Helmand - where U.S. Marines and British soldiers are battling a resilient insurgency - came a day after the first protests over Sunday's massacre flared in the eastern city of Jalalabad. Some 2,000 demonstrators chanted "Death to America" and demanded Karzai reject a planned strategic pact that would allow U.S. advisers and possibly special forces to remain beyond the pullout of most NATO combat troops by the end of 2014.
DEMAND FOR TRIAL in AFGHANISTAN
The U.S. military hopes to withdraw about 23,000 soldiers from Afghanistan by the end of the coming summer fighting season, leaving about 68,000.
In the two Panjwai district villages where the weekend massacre took place, U.S. troops remained confined to the compound where the soldier was based, and people in the area demanded a trial in Afghanistan under Afghan law.
"They have to be prosecuted here. They have done two crimes against my family. One they killed them, and secondly they burned them," said Wazir Mohammad, 40, who lost 11 members of his family in the incident.
A cleric, Neda Mohammad Akhond, said he believed the shootings may have been retaliation for an insurgent landmine attack on a U.S. convoy in the days before the massacre.
"They asked people to come out of their homes and warned them they would avenge this," Akhond said.
There was no independent verification of an earlier attack.
NATO officials said it was too early to tell if the U.S. soldier would be tried in the United States or Afghanistan if investigators were to find enough evidence to charge him, but he would be tried under U.S. laws.
Typically, once an initial investigation is completed, prosecutors decide if they have enough evidence to file charges and then could move to a so-called Article 32 or court martial.
While Afghan members of parliament called for a trial under Afghan law, Karzai's office was understood to accept that a trial in a U.S. court would be acceptable provided the process was transparent and open to media.
(Additional reporting by Ahmad Nadem in KANDAHAR and Mirwais Harooni in KABUL, Writing by Rob Taylor, Editing by Robert Birsel)