MOSCOW, 19 Feb (REUTERS) -- Separatist leaders in eastern Ukraine have ordered a full military mobilisation, further escalating tensions in the region after Washington said Moscow would invade within days, and Ukraine’s president headed to Europe to drum up support.

As the Kremlin said that Vladimir Putin will oversee major military drills along Ukraine’s borders on Saturday, the head of the pro-Russian separatist government in the Donetsk region, Denis Pushilin, released a statement announcing a war footing and urging reservists to show up at military enlistment offices.

Shortly after the announcement on Saturday morning, a second separatist leader, Leonid Pasechnik of the self-proclaimed Luhansk People’s Republic (LNR), signed a decree calling for a full military mobilisation, according to Reuters.

The statements added to the febrile situation in eastern Ukraine, where the rebels have ordered mass evacuations in the face of alleged shelling and mortar attacks by the Ukrainian army.

The US president, Joe Biden, renewed his warnings on Friday night that a Russian invasion of its neighbour could happen at any time, and said that claims by pro-Moscow separatists in eastern Ukraine that they were under attack by Ukrainian government forces were “fabricated”.

Monitors from the Organization for Security and Co-operation in Europe said on Saturday they had seen a significant rise in the number of attacks along the front line, particularly in the separatist areas of Donetsk and Lugansk, fuelling western fears that Moscow could use it as a pretext for an invasion.

The Pentagon also said that 40% of Russia’s estimated 150,000-strong forces on the border were in “attack position”. US officials think that the total number of troops is 190,000 when Ukrainian pro-Moscow rebels are included in the figure.

Compounding western concern about Russia’s military buildup, Russia’s defence ministry announced that Putin would personally oversee drills on Saturday that will involve multiple practice missile launches.

The Kremlin denies it has any plans to attack Ukraine and added to the war of words on Saturday morning by rejecting US allegations that it was responsible for cyber-attacks on Ukrainian banking and government websites earlier in the week.