Kiev (AFP) - Fears may be rising in the West that eastern Ukraine could be plunged back into all-out conflict but a new offensive by pro-Russian forces is unlikely any time soon, analysts said Thursday.

The amount of military hardware being moved into the war-torn region is insufficient for a major operation, which would probably not be launched during Ukraine's harsh winter, experts told AFP.

Instead, the deployments may be designed to deter Ukraine from launching a bid to reclaim the territories or send a message to a domestic audience in Russia.

"There is a positional war of attrition going on. Any large-scale offensives are highly unlikely," said Pavel Felgenhauer, an independent military analyst based in Moscow.

"For a major operation, you need thousands of tanks. There are a lot less than that -- and mainly just artillery."

In recent days, a string of Western powers have spoken out over fears that Russia is sending reinforcements to eastern Ukraine, parts of which have been taken over by separatists loyal to Moscow.

The Kremlin denies any involvement in the conflict but supports the rebels politically. A nominal ceasefire punctuated by frequent spells of fighting has been in place in eastern Ukraine since September.

NATO's commander in Europe, US General Philip Breedlove, said Wednesday that "columns of Russian equipment, primarily Russian tanks, Russian artillery, Russian air defence systems and Russian combat troops" were entering Ukraine.

The Organization for Security and Cooperation in Europe (OSCE) has warned that violence could get worse and is concerned about tanks and heavy weaponry witnessed by its observers moving through east Ukrainian territory held by separatists.

And Ukraine's government says it is preparing for "combat operations".

- Could last for 'decades' -

Breedlove said NATO's "first guess" was that Russia may be trying to wipe out stubborn Ukrainian resistance at strategic hotspots across rebel territory, such as Donetsk airport, in order to control a "more contiguous, more whole and capable pocket of land" that could be held long-term.

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But Konstantin Kalachev, head of Moscow-based Political Expert think-tank, argued that it would not benefit the Kremlin to move "from a semi-frozen conflict to a hot phase".

"What is happening now is not the build-up to an offensive," he said.

"Russia needs a military presence (in Donetsk and Lugansk) in order to start marshalling these people (the separatists) and to force the field commanders to work together."

He added that the "sabre rattling" of sending in extra troops and equipment also aimed to "stop Ukraine thinking about trying to reclaim the territories where the coalmines are".

Ukraine's economy has been hit hard by the unrest, which has been going on since April and claimed over 4,000 lives, and coal mining is one of the country's major industries.

Felgenhauer suggested that the rebels see the current ceasefire deal as a "betrayal" and were trying to provoke an escalation in fighting.

"They're trying to show to the Kremlin that Kiev is getting ready to attack," he said. "Their appeals seem to have worked somehow and Russia has sent in some weaponry, mainly artillery."

But he believed that the volume of forces and hardware being deployed "are completely inadequate for an offensive and the time of year is not suitable."

"In theory, there is a possibility of major actions after New Year, in January or February. But I doubt it will happen in the winter -- more likely spring," he said.

Natasha Kuhrt of the Department of War Studies at King's College London described the movements as an "intimidation tactic" targeted at people watching the situation from Russia.

"I don't actually think it's going to go further than that," she said. "It's also a way of saying domestically that 'we have to stay tough.'"

Others warned that, despite recent movements, the conflict in the east of Ukraine could still drag on for many years to come.

Philippe Migault, director of research at the Institute of International and Strategic Relations in Paris, dismissed the idea of a fresh offensive, saying such a move would risk "losing everything".

He added that a frozen conflict "is in the interests of separatists and of Russia -- a form of political fait accompli. It could go on for decades."