Moscow on Saturday launched a “counter-terror operation” in three border regions adjoining Ukraine to halt Kyiv’s biggest cross-border offensive in the two-and-a-half-year conflict. Ukrainian units stormed across the border into Russia’s western Kursk region on Tuesday morning in a shock attack and have advanced several kilometers, according to independent analysts. Russia has deployed additional troops and equipment, including tanks, rocket launchers and aviation units to stop the advancing troops. Russia’s national anti-terrorism committee said late Friday it was starting “counter-terror ope…