Fears that Russia was massing troops on Ukraine`s border grew today ahead of a visit by NATO`s secretary general, as an air strike hit the main eastern city where Kiev troops are besieging rebels.
NATO and Poland both warned that Russia may be gearing up to invade its former Soviet neighbour, despite strong denials from Moscow.
The first air strike on rebel-held bastion Donetsk came as Ukrainian forces said they were preparing to liberate the city, although they also reported their highest death toll in weeks in the face of fierce rebel bombardments.
Today, NATO warned that Russia had increased the number of "combat-ready" troops on its border with Ukraine to 20,000 from 12,000 in mid-July.
"This is a dangerous situation," NATO spokeswoman Oana Lungescu said, warning that "Russia could use the pretext of a humanitarian or peacekeeping mission as an excuse to send troops into eastern Ukraine."
Poland`s Prime Minister Donald Tusk said "the threat of a direct intervention (by Russia into Ukraine) is certainly greater than it was even a few days ago."
Moscow said those making the claims about their troop movements were "selling soap bubbles".
"Movements of such forces of thousands of troops and equipment are not possible in such a short time," said Russian defence ministry spokesman Igor Konashenikov.
Against this backdrop, Kiev said NATO chief Anders Fogh Rasmussen will visit on Thursday at the invitation of President Petro Poroshenko.
The visit is meant to discuss NATO-Ukraine partnership but Rasmussen has also ratcheted up the rhetoric lately, saying in an interview on Sunday that NATO would draw up new defence plans in the face of "Russia`s aggression".
The West accuses Russia of supporting and instigating the insurgency in eastern Ukraine, sending tensions with Moscow soaring to their highest point since the Cold War.
The US and European Union have slapped a range of tough sanctions on Moscow, with Switzerland, Japan and Canada following suit, potentially pushing Russia`s fragile economy towards recession.
But Russian President Vladimir Putin struck back with import bans and restrictions on agricultural products from countries that have targeted Moscow.