KABUL — The United States must confront Russia for providing weapons to the Taliban for use against American-backed forces in Afghanistan, top U.S. military officials said Monday. At a news conference with Defense Secretary Jim Mattis at his side, Gen. John Nicholson, the American commander in Afghanistan, wouldn’t provide specifics about Russia’s role in Afghanistan. Mattis met with President Ashraf Ghani and other senior government officials just hours after the nation’s defense minister and Army chief resigned over a massacre of more than 140 Afghan troops at a military base on Friday. Nicholson recently told Congress that he needs a few thousand more troops to keep Afghan security forces on track to eventually handling the Taliban insurgency on their own.