NATO announced on Wednesday that it was concerned that 20,000 Russian combat troops gathering on the Ukraine-Russia border were going to cross into Ukraine. NATO speculated that the troops would enter the country as peacekeepers to stop attacks on East Ukraine by West Ukraine forces.

The civil war in Ukraine, pitting the government of Kiev backed by the US and EU against East Ukraine separatists backed by Russia, has been escalating recently with Kiev’s military incursions into East Ukraine catching numerous civilians in the crossfire. The carnage from the fighting combined with the downing of Malaysian Flight 17 by parties still unknown has pushed Ukraine into a state of chaos and international focus.

After losing Crimea the government in Kiev seems determined to keep East Ukraine under its central authority – a task that looks increasingly hopeless.

NATO said early this year that Russia had amassed some 40,000 troops close to the Ukraine border. By June, the number had dropped to less than 1,000, but then Russia started building the force up again. A NATO military officer, speaking on condition of anonymity, said that early this month Russia had significantly increased the number of troops near the Russian border.

The roughly 20,000-strong troop presence included tanks, infantry, artillery, air defense systems, as well as logistics troops, special forces, and various aircraft, the officer said.

If Russia entered East Ukraine to protect the separatists it is unclear what the government in Kiev would do. Military strikes on Russian forces would almost certainly lead to massive retaliation by the superior Russian military. The government in Kiev would certainly ask for US and NATO military assistance – but would they get it? Russia has already mostly ignored US sanctions, instead imposing counter-sanctions against US products entering Russia, so the only leverage US and NATO would have is to threaten to use military force. Where that road ends no one knows.

A Russian peacekeeping operation in Ukraine might also expand out from protecting separatists to regime change in Kiev. One of Russia’s most recent humiliations was being cut out of influence in the NATO operation in Kosovo. Is Russia planning to even the score with a full invasion and peacekeeping operation that brushes aside NATO?