The Ukrainian President Viktor Yushchenko has promised to pass a law outlawing Nato military bases on his country's territory just a day after Vladimir Putin had threatened to point nuclear missiles at Ukraine if the country joined the alliance.
Last month Mr Yushchenko and Ukraine's pro-Western Prime Minister Julia Timoshenko, the pair who led the Orange Revolution in 2004, asked Nato to begin considering Ukrainian membership – a move hugely controversial among a large section of the Ukrainian population and strongly criticised by Moscow.
After meeting the Ukrainian leader on Tuesday, Mr Putin said that Nato membership could well mean that Nato military bases or elements of a planned US missile shield would be placed in Ukraine, and that Russia would be forced to respond. "I am not only terrified to utter this, it is scary even to think it," said Mr Putin. "Russia would have to target its offensive rocket systems at Ukraine."
Russian officials have previously suggested that were Ukraine to join Nato, Russia would introduce a visa regime for Ukrainian citizens, complicating the lives of millions of Ukrainians who work in Russia or have relatives there.
Mr Putin's comments came after the two presidents agreed to a last-minute deal to keep gas flowing between the two countries. Russia had threatened to cut off gas to Ukraine unless a £750m debt was paid for earlier supplies. This caused alarm in European countries, which receive much Russian and central Asian gas through pipes that go through Ukraine. Gas was cut off in 2006 when Russia demanded that Ukraine pay closer to market prices for its gas in what analysts said was retaliation for Ukraine's pro-Western course. Previously, the country received gas at heavily subsidised rates.
Ms Timoshenko, who began a second stint as prime minister late last year and has strongly criticised Russia on many occasions, has said that the debt this time was caused by shady intermediary companies that were brought into the equation after the 2006 stand-off. She demanded that Ukraine buy gas from the Russian company Gazprom directly, rather than using the current opaque system.
The deal reached in Moscow this week seems to satisfy both sides for now, but Russian-Ukrainian relations are still fraught with difficulty. Ukrainian citizens in the Russian-speaking eastern part of the country have complained that a raft of discriminatory legislation has been passed in recent months. One of the most controversial was a law stating that cinemas could only show films that were dubbed into Ukrainian. Many cinemas in the Russian-speaking parts of the country have simply closed down.
Earlier in the week, 50 MPs from the Party of the Regions stopped the work of the Ukrainian parliament by blocking the rostrum and waving balloons in the colour of the Ukrainian flag inscribed with "No to Nato!" The party is headed by Viktor Yanukovich, who was defeated by Mr Yushchenko in the re-run presidential election that followed the Orange Revolution.
He is demanding a plebiscite on Nato accession and yesterday in Moscow, Mr Yushchenko appeared to accede to that demand, saying that a referendum would be held "in good time".