MOSCOW—Russia on Friday strongly reaffirmed its demand that NATO doesn’t expand eastward despite the rejection of that by the military alliance amid a Russian troop buildup near Ukraine. Foreign Minister Sergey Lavrov warned that Moscow wouldn’t wait indefinitely for the Western response, saying he expects the United States and NATO to provide a written answer next week. Lavrov described Moscow’s demands for binding guarantees that NATO will not embrace Ukraine or any other ex-Soviet nations, or station its forces and weapons there as essential for the progress of diplomatic efforts to defuse soaring tensions over Ukraine. He argued that NATO’s deployments and drills near Russia’s borders pose a security challenge that must be addressed immediately. Amid the tensions, Ukraine sustained a massive cyberattack Friday, which hit websites of multiple government agencies. This week’s negotiations in Geneva and a related NATO-Russia meeting in Brussels were held amid a significant Russian troop …