Pro-Moscow rebel forces in eastern Ukraine, backed by Russian tanks and armored personnel carriers, battled government forces on two fronts Thursday, a Ukrainian military official said.
The fighting was taking place southeast of Donetsk, and along the nation's southern coast in the town of Novoazovsk, about 12 miles (20 km) from the Russian border, according to Mykhailo Lysenko, the deputy commander of the Ukrainian Donbas battalion, reports GHN based on CNN
"This is a full-scale invasion," Lysenko said, referring to the fighting in the south.
U.S. officials also said Russian troops were directly involved in the latest fighting, despite Moscow's denials.
Intelligence now indicates that up to 1,000 Russian troops have moved into southern Ukraine with heavy weapons and are fighting there, a U.S. official told CNN on Thursday.
Ukraine's National Defense and Security Council said that Russian forces were in full control of Novoazovsk as of Wednesday afternoon.
Russia's military fired Grad rockets into the town and its suburbs before sending in two convoys of tanks and armored personnel carriers from Russia's Rostov region, it said in a statement
"Ukrainian troops were ordered to pull out to save their lives. By late afternoon both Russian convoys had entered the town. Ukraine is now fortifying nearby Mariupol to the west," the NDSC said.
A number of villages in the Novoazovsk, Starobeshiv and Amvrosiiv districts were also seized, it said.
Novoazovsk is strategically important because it lies on the main road leading from the Russian border to Ukraine's Crimea region, which Russia annexed in March. Separatist leaders in the Donetsk and Luhansk regions then declared independence from Kiev.
The NDSC also warned that a strong counterattack is expected in the Shahtarsk-Illovaysk area, near where Malaysia Airlines Flight 17 is believed by the West to have been shot down by rebels armed with Russian-made weapons.