US and Ukrainian sources report that Russian heavy weapons have crossed into S. Ukraine, apparently to aid rebels in what is shaping up as a major counteroffensive on a new front along the border.  The sources say this is a “stealth invasion.” With battles raging in the northern areas of Luhansk and heavy fighting at Donetsk airport, the Russian incursion appears to focus on Novoazovsk in the south. Ukrainian forces are described by Western reporters to be abandoning vehicles and ammunition in their retreat from the new sector. The US State Department said the Russians were driving in with tanks and rocket launchers.