The Russian president also announced that he is pulling troops from the borders, a claim not confirmed by an independent verification. Moscow's dependence on Ukrainian-made weapons appears to be behind Putin's change of heart. Russia is in fact Ukraine's fourth largest weapons export market. About 80 per cent of Russian nuclear warheads need parts made in the Ukraine.

Kyiv (AsiaNews) - In an unexpected turn of events, Russian President Vladimir Putin now seems to have changed his mind over the Ukraine.

During a meeting yesterday with Organisation for Security and Cooperation in Europe (OSCE) chief Didier Burkhalter, Mr Putin said that Russian forces had pulled back from the borders. He also called on separatists to halt their referendum on independence, and expressed support for Ukraine's presidential election on 25 May.

Although a Pentagon spokesman yesterday said that the US had not seen any change in the Russian force posture along the Ukrainian border, Putin's new position represents a major shift.

Until recently, the Russian leader had backed separatists in Crimea and then in eastern Ukraine. Just a few days ago, his spokesman had said that an election in the Ukraine would be absurd. Now, he is calling those same elections a move "in the right direction".

For some observers, Putin's changing tune is due to US and EU threats to increase economic sanctions against Russian leaders and companies.

They note that eastern Ukraine needs to cool off because it is home to the most valuable assets of that nation's defence industry.

Following a trade deal signed from two decades ago, more than 50 Ukrainian factories cater to Russian military needs, churning out air cargo transporters, helicopter engines and other hardware.

Russia's US$ 15 billion agreement with ousted Ukrainian President Viktor Yanukovych in December included defence-related industries.

More than half of Russia's nuclear arsenal was built in Ukraine or is equipped with a Ukraine-made navigation systems.

"We hope the situation won't develop into a complete interruption of cooperation," Putin said since the loss of Ukrainian supplies would negatively impact Russia's defence systems.

If supplies stop, there will be "a very serious problem with some weapon systems," Siemon Wezeman, a senior researcher at the Stockholm International Peace Research Institute, or SIPRI, said yesterday.

At the same time, Ukraine, which is struggling to keep its economy afloat, cannot do without US$ 1.3 billion in annual weapons exports.

According to SIPRI, the former Soviet republic ranked eighth among the world's supplier of arms in 2009-2013.

During that same period, Russia was the fourth-biggest customer for Ukrainian defence-related products after China, Ethiopia and Pakistan.

As much as 80 percent of Russia's nuclear warheads are loaded in missiles designed or manufactured in Ukraine during Soviet times.

Therefore, Putin may yet find a peaceful end to the current crisis in order to prevent disruption to supplies.

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