Ukrainian President Viktor Yushchenko met Russian President Vladimir Putin Feb. 12 and reached a deal to begin paying off Ukraine's gas debt starting Feb. 14, avoiding a threatened cutoff in supplies that had rattled consumers in the European Union.

However, later the same day Putin warned that Russia could aim nuclear missiles at Ukraine if the former Soviet republic joins NATO and accepts the deployment of anti-missile defenses on its territory.

It was Putin's strongest warning to date against Ukraine's efforts to join the Western military alliance.