The Pentagon says it cannot confirm the reports. It almost certainly knows a lot more than that. But officials do not want to start a process of escalation that will be hard to reverse.

The priority will be establishing the facts, or a narrative NATO can live with. They may not be the same thing.

Russian missiles kill two people in Poland

There may be an innocent explanation. Russian fired more than 85 missiles during the day. Precision-guided, but they can malfunction.

But for nine months Russia has managed to avoid hitting Ukraine's neighbours. Was it a coincidence this happened when world leaders were meeting without Vladimir Putin for the G20 in Bali?

It may be a plausibly deniable deliberate act. An attack made to look like an accident, testing NATO while world leaders are gathered on the other side of the world.

If that is the case it will require a response. Anything less would be a sign of weakness - and that could embolden Russia to take more provocative attacks in future. But overreacting risks dangerous escalation.