Pro-Russian rebels downed a military helicopter in eastern Ukraine, killing a general and 13 troops, as a spokesman for U.S. President Barack Obama blamed “outside” assistance in providing weapons. Insurgents used a shoulder-fired missile to shoot down an Mi-8 transport chopper amid heavy fighting in Slovyansk, 100 miles (160 kilometers) from the Russian border, Speaker Oleksandr Turchynov told Ukraine’s parliament yesterday. “We are concerned that this indicates separatists continue to have access to advanced weaponry and other assistance from the outside,” White House spokesman Jay Carney told reporters in Washington . Ukrainian forces used aviation and artillery assets to “destroy” the rebel unit that downed the helicopter, the Interior Ministry ’s National Guard unit said in a statement. The surge in fighting produced a new round of finger-pointing between the U.S. and Russia. Russia demanded that Ukraine halt its “fratricidal war” and withdraw troops from the mainly Russian-speaking region […]