On Friday, as a Russian "aid convoy" of 280 trucks crossed the Ukrainian border, NATO said that the Russian military was sending Russian-manned artillery units into rebel-held eastern Ukraine, which certainly sounds like a formal military invasion, though NATO and the US have declined to call it that. This comes one week after a separate "incursion" of Russian military forces had crossed into eastern Ukraine, raising surprisingly difficult to answer questions about whether this now constituted a formal war between Russia and Ukraine.

Did Russia really invade Ukraine outright? Is this now an open war? Here is a running account of what we know and what we don't know.

What we know

— NATO says Russian artillery crossed into Ukraine and are attacking Ukrainian forces. The US and Ukraine have been saying for weeks that Russian artillery were firing into Ukraine at Ukrainian military forces from within Russia, but they now appear to have moved within Ukraine itself. The artillery are being used to support Russia-backed separatist rebels who control territory in eastern Ukraine.

— The US and NATO are condemning, but won't call it an invasion. When asked whether this constitutes a formal military invasion, the Pentagon's press secretary dodged, saying, "It's certainly unauthorized entry." The US and NATO have called for the Russian forces and "aid" convoy to pull out of Ukraine.

— Russia sent a "humanitarian convoy" to Ukraine, but it seems pretty military. 280 Russian trucks, flanked by attack helicopters, have been moving across the Ukrainian border. Russia says they're carrying humanitarian assistance for the people of east Ukraine. Ukraine fears it's a stealth invasion force. Russia opened up the trucks to journalists, and the BBC reported that they were mostly empty. The convoy earlier stopped at a Russian military base.

— A pro-Russia rebel leader boasted of receiving 30 tanks and 1,200 troops from Russia. Alexander Zakharchenko, who took over the largest rebel group last week, announced on August 16th that "At present, moving along the path of this corridor [from Russia] . . . there are 150 items of combat hardware, 30 of which are tanks" as well as "1,200 individuals who underwent four months of training in the Russian Federation." That certainly sounds like a Russian invasion force.

— The United Nations Security Council called an emergency meeting. It will be held at 3pm eastern time on Friday. Russia is one of the five permanent members of the Security Council, which means it has unilateral veto power.

— Ukraine claims to have destroyed Russian vehicles on August 14. In a phone call with British Prime Minister David Cameron, Ukrainian President Petro Poroshenko claimed Ukraine's military had fired on and destroyed a "significant" portion of "Russian military machines in Ukraine," allegedly with artillery. On August 15, Nato announced it had tracked a "Russian incursion" into Ukraine.

— Russia has been backing separatist rebels in eastern Ukraine for months. The pro-Russia rebels, who are in many cases Russian themselves, declared independence in cities like Donetsk and have been fighting Ukrainian government forces.

—The Ukrainian military is making a big push to re-take eastern Ukraine. After months of low-level fighting with the rebels, and after the rebels appeared to shoot down civilian airliner flight MH17 over eastern Ukraine, the Ukrainian military has been moving aggressively to expel them. That might help explain why Russia would escalate as well.

— Russia used a stealth invasion force to seize Crimea in March, by quietly sending unmarked special forces into the Ukrainian region. The Russian troops quickly seized the region, expelled Ukrainian forces, held a fraud-ridden referendum on seceding, and annexed Crimea. There are fears Moscow may attempt the same here.

What we don't know

— Whether Russian tanks crossed into Ukraine on August 14. If so, that would be a major escalation from the past practice of sending small numbers of unmarked troops, and a big step toward an overt war.

— Whether Ukraine is actively firing back at Russian-flagged forces. Ukraine described firing back at the August 14th "incursion," which Russia denies exists. Now that Russian forces appear to be in Ukraine more overtly, if Ukraine returns fire this may provide Moscow with an excuse to more fully invade.

— Whether the Russian aid convoy is part of a secret invasion force. That's what Ukrainian officials say, and the fact that the trucks appear to be empty is highly suspect, but it's still not clear whether or not the 280-truck convoy is part of some secret plot or just there deliver humanitarian supplies, as Moscow says.

— What Russia does next. Again assuming the incident Ukraine described happened, it's totally unclear how Russia would respond. Will they escalate to full warfare with Ukraine? That remains to be seen.

— Could Russia try to annex eastern Ukraine? That's what they did in Crimea, and Russia has been backing separatist rebels in eastern Ukraine for months. But that would be a big step, and even riskier than the Crimea annexation.

— How will the US and Europe respond? American and European leaders have ratcheted up economic sanctions on Russia to deter it from invading, but have been hesitant to directly arm or supply Ukraine, for fear of getting sucked into a war. It's not clear how they'll respond if open war breaks out between Russia and Ukraine.