A new study says war in Afghanistan since the 2001 U.S.-led invasion overthrew the Taliban regime has killed almost 100,000 people, and wounded the same number.

The study, called Costs of War and produced by Brown University's Watson Institute for International Studies, looks at war-related deaths, injuries and displacement in Afghanistan and Pakistan from 2001 to last year, when international combat troops left Afghanistan.

Civilian and military deaths in both countries total almost 149,000 people killed, with 162,000 seriously wounded, it says.

Noting a rise in annual figures for killed and wounded in recent years, the report's author, Neta Crawford, says the war in Afghanistan "is getting worse."

The United Nations said civilian casualties rose 16 percent in the first four months of 2015, with 974 people killed.