Russian tanks launch an attack in southeastern Ukraine

Two columns of Russian tanks rolled into southeastern Ukraine today, following a rocket attack on a border post. The outmatched Ukrainian border guards fled, according to a top Ukrainian official.

Officials in Kiev say 1,000 Russian troops have marched into Ukraine, but Brig. Gen. Nico Tak said that was a conservative estimate. Another 20,000 Russian troops are amassed just over the border, he said. Russia’s ultimate goal, Tak suggested, was to bolster the pro-Russian separatists and create indefinite destabilization in the country.

The strategic southeastern town of Novoazovsk now appears to be under rebel control, creating a third front in the ongoing conflict, which until now had been limited to the northeast.

In announcing the incursion, Ukrainian President Petro Poroshenko urged his citizens not to panic because that works to the Russians’ advantage. He cancelled a foreign trip and called an emergency meeting of his security council.

“Today the president’s place is in Kiev,” he said.

Ukraine’s Col. Andriy Lysenko, a top NATO official, said the Russian missiles were fired on Ukrainian positions at 11 a.m. An hour and a half later, the two columns of tanks and other vehicles attacked after entering Ukraine from Veselo-Voznesenka and Maximovo, in Russia’s Rostov region.

“Over the past two weeks we have noted a significant escalation in both the level and sophistication of Russia’s military interference in Ukraine,” Tak said. “Russia is reinforcing and resupplying separatist forces in a blatant attempt to change the momentum of the fighting, which is currently favoring the Ukrainian military.”

Though Russia has said that any of its citizens fighting with the separatists are volunteers, new NATO satellite images suggest the Russian troops operating in Ukraine’s territory brought sophisticated heavy weaponry with them. Tak said the satellite images are “the tip of the iceberg” when it comes to the scope and sophistication of Russian involvement.

“This is highly sophisticated weaponry that requires well-trained crews, well-trained command and control elements, and it is extremely unlikely that this sort of equipment is used by volunteers,” he said.

The United States has accused Russia of setting up the separatist rebellion and supplying arms. Insurgency leader Alexander Zakharchenko told Russian national television between 3,000 and 4,000 Russians have fought in the conflict since it began in April.

The rebels entered Novoazovsk, which sits on the road connecting Russia to the Russian-annexed Crimean Peninsula, on Wednesday after it suffered three days of shelling. The rebels had to enter the town through Russia, and the new front raises fears the insurgents want to connect Russia and Crimea, giving them control over the Sea of Azov and potential gas and mineral supplies.

National Guard spokesman Ruslan Muzychuk said Ukrainian reinforcements are taking up positions in Mariupol, about 20 miles from Novoazovsk.

“The positions are being strengthened,” he said. “The road from Novoazovsk to Mariupol is under the control of Ukrainian troops.”

On Monday, Ukrainian forces captured 10 soldiers from a Russian paratrooper division about 12 miles from the Russian border. And in Donetsk, the largest city controlled by the insurgents, 11 people were killed by overnight shelling, according to city officials.

The UN Security Council will hold an emergency meeting on the situation in Ukraine this afternoon.

The Associated Press contributed to this report.