British Prime Minister David Cameron has described the alleged killing of Afghan civilians by a U.S. soldier as “absolutely dreadful.” Speaking Monday, Mr. Cameron said the incident will have an impact but that Britain’s aims in Afghanistan remain the same.

Britain's Prime Minister David Cameron (L) speaks during a joint news conference with Ireland's Taoiseach Enda Kenny in 10 Downing Street, London, March 12, 2012

Mr. Cameron was speaking at a press conference Monday, one day after a U.S. soldier allegedly killed 16 civilians during a shooting spree.

Mr. Cameron said the killings must not derail the work that international forces are doing in Afghanistan.

“It is worth remembering why we are in Afghanistan," Cameron said. "We're there to train up the Afghan army and police so that that country is able to look after its own security and make sure that country isn't a haven for terrorists without having foreign troops on its soil. That's what we all dearly want."

But some British politicians raised questions both about Britain’s role in what one lawmaker described an “unwinnable war” and about the care taken over soldiers’ mental stability.

In Afghanistan, the anger has been widespread. Afghan lawmakers said they have “run out of patience” with international troops and the Taliban vowed in an online statement to avenge Sunday’s deaths.

Analysts say reprisal attacks are likely - and that U.S. troops are unlikely to be the only target.

David Livingstone is an expert in international security at the London-based research group Chatham House.

"Foreign armies, they will be grouped as one," Livingstone said. "And, of course, in Helmand Province you have got some of the most fervent and some of the most dangerous of Taliban gangs. You would expect to see reprisals levied at whomever, whichever nations are there under the NATO banner."

Prime Minister Cameron is due to visit the United States this week for talks with President Barack Obama.

Livingstone says Afghanistan will be their number one discussion point. "I think they see very much eye to eye," he said. "The mission is very, very tight between the two nations under the banner of NATO, and I don't see any differences between them either politically, operationally, or tactically on the Afghan question in itself."

German Chancellor Angela Merkel, in Afghanistan Monday to visit German troops, spoke to Afghan President Hamid Karzai on the telephone and expressed her condolences.