30 tanks and 1,200 troops just crossed from Russia into Ukraine, according to the rebels

Eastern Ukraine’s main pro-Russia rebel group, the Donetsk People’s Republic, posted a video on Saturday in which the group’s leader announced they had received 30 tanks, 120 other armored vehicles, and 1,200 troops from across the Russian border.

While not confirmed, this certainly sounds like a Russian invasion force, something that NATO has warned for two weeks that Moscow could be on the verge of attempting.

While the rebel leader did not explicitly say the troops and equipment were Russian military, he strongly implied as much, saying that the troops included “individuals who have gone through training over a four-month period on the territory of the Russian Federation and who have been introduced here at the most decisive moment.”

If true, this would be by far Russia’s most overt act of war in eastern Ukraine, where it has for months supported, trained, and armed separatist rebel factions. Russia has been dramatically increasing its involvement over the past month, including by reportedly shelling Ukraine with its artillery and, many suspect, providing rebels with the anti-air missile systems that were used to shoot down Malaysian Airlines flight MH17.

Here is the video, posted on Saturday to a pro-rebel YouTube account but reportedly recorded the day before. Also on Friday, Ukraine claimed it had shelled and destroyed a number of Russian military tanks attempting to cross the border.

There has been a flurry of military activity along the Russia-Ukraine border since late Thursday, when a Russian government aid convoy of 280 trucks — widely suspected to be a stealth invasion force, and flanked by military escort — approached the border. On Friday, Ukraine and NATO both announced that Russia had sent an “incursion” force across the border, which this video would seem to back up.

In the weeks after flight MH17 was shot down over eastern Ukraine, the Ukrainian government has pushed aggressively to retake rebel-held territory there. Moscow may be escalating in turn to prevent the Russia-backed rebels from getting overrun.