Among the foreign powers involved in the war, Britain has suffered casualties second only to the 1,126 of the United States. But the British losses are higher proportionally when set against the two nations’ populations, overall military manpower and Afghanistan deployments. Britain, with about 60 million people, has nearly 10,000 troops in Afghanistan.

In both countries, the governments have come under political pressure from faltering public support for the war.  The British PM. David Cameron — who visited British troops in Helmand 10 days ago — reflected the growing sense that his government, in office barely six weeks, is resolved not to allow itself to be dragged into an open-ended military commitment.

“Of course, the 300th death is no more or less tragic than the 299 that came before,” Mr. Cameron said. “But it is a moment, I think, for the whole country to reflect on the incredible service and sacrifice and dedication that our armed services give on our behalf.”

“We are paying a high price for keeping our country safe, for making our world a safer place, and we should keep asking why we are there and how long we must be there,” he added. “The truth is that we are there because the Afghans are not yet ready to keep their own country safe and to keep terrorists and terrorist training camps out of their country. That’s why we have to be there."