Nato said yesterday there was a “high probability” that Russia could launch an invasion of eastern Ukraine under the guise of a humanitarian operation, but a defiant President Vladimir Putin said Moscow was sending an aid convoy into the country.

With Ukraine reporting Russia has massed 45,000 troops on its border, European Commission President José Manuel Barroso also warned Putin against any military intervention in the country.

We see Russians developing pretext under the guise of a humanitarian act

The past week has seen increasingly urgent warnings from Kiev and Western countries that Putin appeared to be planning an invasion.

Western countries said Putin – who has whipped up the passions of Russians with a relentless nationalist campaign in state-controlled media since annexing Ukraine’s Crimea peninsula in March – could invade to head off a humiliating rebel defeat.

The EU chief delivered his message in a telephone call to Putin.

“President Barroso warned against any unilateral military actions in Ukraine, under any pretext, including humanitarian,” the Commission said in a statement. However, the Kremlin made clear that Moscow, which has expressed its concern about Russian speakers in eastern Ukraine as Kiev forces try to crush pro-Russian rebels, would indeed send aid.

Kiev said it was in the “final stages” of recapturing the eastern city of Donetsk – the main base of the separatist rebels in a battle that could mark a turning point in a conflict that has caused the biggest confrontation between Russia and the West since the Cold War.

Nato Secretary-General Anders Fogh Rasmussen said there was no sign Russia had withdrawn the troops it had massed at the Ukrainian frontier. Asked in a Reuters interview how he rated the chances of Russian military intervention, Rasmussen said: “There is a high probability.

“We see the Russians developing the narrative and the pretext for such an operation under the guise of a humanitarian operation, and we see a military build-up that could be used to conduct such illegal military operations in Ukraine.”

Nato believes any Russian humanitarian mission would be used as a pretext to save the rebels, who are fighting for control of two provinces under the banner of “New Russia”, a term Putin has used for southern and eastern Ukraine, where Russian is spoken.

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