CAMP LEATHERNECK, Afghanistan (Reuters) - U.S. Defence 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 officer and wounding three people, a local government spokesman said, as Panetta kicked off his two-day trip in neighbouring Helmand province.
It wasn't clear who was behind the bombing, but the area is a Taliban stronghold.
Panetta's trip had been scheduled before Sunday's shootings in two villages in Kandahar province, but it takes on new meaning as political pressure mounts on Afghan and U.S. officials over the unpopular war, now in its eleventh year.
He was due to speak with troops in Afghanistan, who could become the targets of any backlash over the killings of villagers, including nine children, by a lone American soldier. The Afghan Taliban threatened to retaliate by beheading U.S. personnel.
Panetta will also hold talks with Afghan leaders including President Hamid Karzai as tensions remain high following a spate of incidents including the burning of Korans at the main NATO base in the country last month.
Last weekend, a U.S. Army staff sergeant walked off his base in Kandahar province in the middle of night and gunned down at least 16 villagers, mostly women and children.
Panetta's arrival in Helmand - where U.S. Marines and British soldiers continue to battle resilient insurgents - 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.
Panetta, the most senior U.S. official to visit Afghanistan since the shootings, told reporters at the start of his trip that he believed the U.S. strategy was working and would withstand fallout from the massacre.
"I think we're on the right path now...And what we've got to do is convince people that despite these kinds of events we ought not to allow these events to undermine that strategy," Panetta said on Monday.
The U.S. military hopes to withdraw around 23,000 soldiers from Afghanistan by the end of the coming summer fighting season, leaving around 68,000 soldiers in the country.
In the two Panjwai district villages where the massacre took place, U.S. troops remained confined to the mostly special forces compound where the soldier was based, and local people demanded a trial in Afghanistan under local 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. U.S. and Afghan officials have blamed the killings on a sole rogue soldier.
"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 under U.S. laws.
Typically, once the 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; Editing by Rob Taylor