Nato Secretary-General Anders Fogh Rasmussen said the alliance had seen what he called "a Russian incursion into Ukraine."
Responding to reports that a Russian column had entered Ukraine overnight, the Nato chief said: "It just confirms the fact that we see a continuous flow of weapons and fighters from Russia into eastern Ukraine and it is a clear demonstration of continued Russian involvement in the destabilisation of eastern Ukraine."
Mr Rasmussen also said Europe is becoming more dangerous and less stable.
More top news
The cyclist said the victory was as sweet as his first win as he became the first Briton to win the race three times.
Local police confirmed the explosion, which occurred near Nuremberg.
Temperatures slide a couple of degrees