KABUL — Six NATO service members, including three Americans, were killed today in Afghanistan, making it the deadliest day for the international force in more than two months. The violence underscored warnings casualties will increase as more troops enter the country and step up fighting against the Taliban.

The Americans died in a firefight with militants during an "operational patrol" in southern Afghanistan, U.S. military spokesman Col. Wayne Shanks said. He did not provide their branch of service pending notification of family members.