Afghanistan, battered by worsening security, is reaching out to an old ally and patron—Russia—just as the Kremlin is seeking to reassert its position as a heavyweight on the world stage. President Ashraf Ghani has asked Moscow for artillery, small arms and Mi-35 helicopter gunships for his country’s struggling military, Afghan and Russian officials say, after the U.S. and its allies pulled most of their troops from Afghanistan and reduced financial aid. The outreach has created another opening for the Kremlin, stepping up the potential for confrontation with Washington. East-West relations are already strained over such issues as Ukraine and Middle Eastern policy. “Russia is seizing the opportunity,” a U.S. official said. Beyond such rivalries, however, the move also reflects Russian concerns that the deterioration of security in Afghanistan could destabilize Central Asia—and bring Islamic extremism closer to its own border.