The West faces a new and dangerous era of “constant competition” with Russia that carries a possible “existential threat to our whole being”, Britain’s most senior commander in Nato has warned.

Speaking as events on the grounds showed more evidence that the supposed ceasefire in Ukraine is in danger of collapse, General Sir Adrian Bradshaw, the Deputy Supreme Allied Commander Europe, said the West was facing twin threats from Russian President Vladimir Putin: modern “hybrid warfare” – the use of cyber attacks, political agitation and sabotage – combined with old-style Soviet land-grab tactics.

Ukraine crisis: A timeline of the conflict Show all 23 1 /23 Ukraine crisis: A timeline of the conflict Ukraine crisis: A timeline of the conflict 30 November 2013 Public support grows for the “Euromaidan” anti-government protesters in Kiev demonstrating against Yanukovych’s refusal to sign the EU Association Agreement as images of them injured by police crackdown spread. EPA Ukraine crisis: A timeline of the conflict 20 February 2014 Kiev sees its worst day of violence for almost 70 years as at least 88 people are killed in 48 hours, with uniformed snipers shooting at protesters from rooftops. AFP/Getty Images Ukraine crisis: A timeline of the conflict 22 February 2014 Yanukovych flees the country after protest leaders and politicians agree to form a new government and hold elections. The imprisoned former Prime Minister, Yulia Tymoshenko, is freed from prison and protesters take control of Presidential administration buildings, including Mr Yanukovych's residence. Genya Savilov/AFP/Getty Imageses Ukraine crisis: A timeline of the conflict 27 February 2014 Pro-Russian militias seize government buildings in Crimea and the new Ukrainian government vows to prevent the country breaking up as the Crimean Parliament sets a referendum on secession from Ukraine in May. Sean Gallup/Getty Images Ukraine crisis: A timeline of the conflict 16 March 2014 Crimea votes overwhelmingly to secede from Ukraine and join Russia in a ballot condemned by the US and Europe as illegal. Russian troops had moved into the peninsula weeks before after pro-Russian separatists occupied buildings. EPA Ukraine crisis: A timeline of the conflict 6 April 2014 Pro-Russian rebels seize government buildings in the eastern cities of Donetsk, Luhansk and Kharkiv, calling for a referendum on independence and claiming independent republic. Ukraine authorities regain control of Kharkiv buildings on 8 April after launching an “anti-terror operation” but the rest remain out of their control. EPA/PHOTOMIG Ukraine crisis: A timeline of the conflict 7 June 2014 Petro Poroshenko is sworn in as Ukraine's president, calling on separatists to lay down their arms and end the fighting and later orders the creation of humanitarian corridors, since violated, to allow civilians to flee war zones. Getty Images Ukraine crisis: A timeline of the conflict 27 June 2014 The EU signs an association agreement with Ukraine, along with Georgia and Moldova, eight months after protests over the abandonment of the deal sparked the crisis. LOUISA GOULIAMAKI/AFP/Getty Images Ukraine crisis: A timeline of the conflict 17 July 2014 Malaysian Airlines flight MH17 is shot down over eastern Ukraine, killing all 298 people on board. Ukrainian intelligence officials claim it was hit by rebels using a Buk surface-to-air launcher in an apparent accident. Ukraine crisis: A timeline of the conflict 22 August 2014 A Russian aid convoy of more than 100 lorries enters eastern Ukraine and makes drop in rebel-controlled Luhansk without Government permission, sparking allegations of a “direct violation of international law”. Reuters/Alexander Demianchuk Ukraine crisis: A timeline of the conflict 29 August 2014 Nato releases satellite images appearing to show Russian soldiers, artillery and armoured vehicles engaged in military operations in eastern Ukraine. Nato Ukraine crisis: A timeline of the conflict 8 September 2014 Russia warns that it could block flights through its airspace if the EU goes ahead with new sanctions over the ongoing crisis and conflict EPA Ukraine crisis: A timeline of the conflict 17 September 2014 Despite the cease-fire and a law passed by the Ukrainian parliament on Tuesday granting greater autonomy to rebel-held parts of the east, civilian casualties continued to rise, adding to the estimated 3,000 people killed Reuters Ukraine crisis: A timeline of the conflict 20 October 2014 A 'tactical missile' explosion at a factory sends blast wave across rebel-held cityof Donetsk YouTube Ukraine crisis: A timeline of the conflict 16 November 2014 The fragile ceasefire gives way to an increased wave of military activity as artillery fire continues to rock the eastern Ukraine's pro-Russian rebel bastion of Donetsk Getty Ukraine crisis: A timeline of the conflict 26 December 2014 A new round of ceasefire talks, scheduled on neutral ground in the Belariusian capital Minsk, are called off AFP/Getty Ukraine crisis: A timeline of the conflict 12 January 2015 Soldiers in Debaltseve were forced to prepare heavy defences around the city; despite a brief respite to the fighting in eastern Ukraine, hostilities in Donetsk resumed at a level not seen since September 2014 AFP/Getty Ukraine crisis: A timeline of the conflict 21 January 2015 13 people are killed during shelling of bus in the rebel-held city of Donetsk Reuters Ukraine crisis: A timeline of the conflict 24 January 2015 Ten people were killed after pro-Russian separatists bombarded the east Ukrainian port city of Mariupol AP Ukraine crisis: A timeline of the conflict 2 February 2015 There was a dangerous shift in tempo as rebels bolstered troop numbers against government forces AFP/Getty Ukraine crisis: A timeline of the conflict 11 February 2015 European leaders meet in Minsk and agree on a ceasefire in eastern Ukraine beginning on February 14. From left to right: Belarus President Alexander Lukashenko, Russian President Vladimir Putin, German Chancellor Angela Merkel, France's President Francois Hollande and Ukrainian President Petro Poroshenko. MAXIM MALINOVSKY | AFP | Getty Images Ukraine crisis: A timeline of the conflict 13 February 2015 Pro-Russian rebels in the city of Gorlivka, in the Donetsk region, fire missiles at Ukrainian forces in Debaltseve. Fighting continued in Debaltseve for a number of days after the Minsk ceasefire began. ANDREY BORODULIN | AFP | Getty Images Ukraine crisis: A timeline of the conflict 18 February 2015 Ukrainian soldiers repair the bullet-shattered windshield of their truck as their withdraw from the strategic town of Debaltseve. Following intense shelling from pro-Russian rebels, Ukrainian forces began to leave the town in the early hours of February 18. Brendan Hoffman | Getty Images

Saying that Nato needs to look at a new strategy to counter the “combination of subversion and coercion” used by its former Cold War adversary in Crimea and eastern Ukraine, Sir Adrian cautioned that traditional military threats still exist.

“The danger is that Russia might believe that the large-scale conventional forces which she has shown she can generate at very short notice – as we saw in the snap exercise that preceded the takeover of Crimea – could in future be used not only for intimidation and coercion but potentially to seize Nato territory,” he said. He added that the threat of Russia expanding its strategy could be a tactic to keep Ukrainian forces at bay.

He added: “This use of so-called escalation dominance was of course a classic Soviet technique. The threat from Russia and the risk it brings of a miscalculation resulting in a strategic conflict, however unlikely we see it as being right now, represents an existential threat to our whole being.”

The salvo by the former head of the SAS is the latest a series of warnings by senior Western political and military figures, as tensions with Moscow over the Ukraine civil war show no sign of subsiding.

Ukrainian officials said yesterday that artillery and mortar fire had hit the village of Berdyansk, near the strategically important port city of Mariupol, which is seen as a likely target for the rebels if they renew their offensive. Kiev also claimed Russia had moved 10 tanks and troops into Novoazovsk, near Mariupol.

Both sides insisted the other had violated the ceasefire repeatedly yesterday, and EU President Donald Tusk said there had been “more than 300 violations” of the ceasefire since it was supposed to have begun last weekend. “People are still dying,” he said. He was “consulting European Union leaders on the next steps” which would be designed to “increase further the costs of aggression on eastern Ukraine”.

Ukrainian President Petro Poroshenko showed no signs of trying to damp down feelings and instead claimed yesterday that a top Kremlin aide, Vladislav Surkov, had directed “foreign sniper groups” who killed protesters in Kiev during pro-European Union protests a year ago. Russia dismissed the idea as “nonsense”.

Russia-backed rebels at the entrance in Debaltseve (AP)

Nato officials still hope that the Russian-backed separatists will draw down their assaults following the capture of the strategic hub of Debaltseve, but they also express apprehension that another flashpoint may end the truce. Nato’s top military commander, US Air Force General Philip Breedlove, said he did not think the Minsk accord had ever taken effect. “It is a ceasefire in name only,” he said.

In his speech at the Royal United Services Institute, Sir Adrian said new tactics should be developed to counter Russia’s strategy in Ukraine. This would include stabilising civic institutions in countries along its western borders and countering Moscow’s propaganda, as well potentially taking part in traditional military action.

The British Army has announced the formation of the 77 Brigade, which will use unconventional warfare, including social media, “to fight in the information age”. The 2,000-strong unit, nicknamed the “new Chindits” after the British and Indian force which used unconventional tactics during the Second World War, will be based near Newbury, Berkshire.

Yesterday a parliamentary committee lambasted the UK Government for “sleep-walking” into the crisis. But David Cameron dismissed the suggestion, saying: “I don’t accept this. The responsibility for what has happened in Ukraine lies absolutely squarely with Vladimir Putin and Russia. They destabilised and effectively invaded this country and have caused all the problems that have happened since.”

There have been comparisons between the current situation in Ukraine and the build-up to both world wars.

Tim Ripley, a defence analyst, said it was “pretty obvious” that the pro-Russian forces wanted to take over the strip of land between the rebel-held east of Ukraine and Crimea, which was annexed by Russia last year. “If this is [a rerun of] 1939, Putin will have his tanks in Kiev by Easter,” Mr Ripley said.

He said Ukraine would stand little chance. “The unwillingness of the West to provide military assistance to Ukraine puts in doubt its existence in its current form. Their ability to withstand more of this must be in question. Their army is being chewed to bits. Their air force is gone, shot out of the sky. It’s nowhere to be seen.”

Timeline: Ukraine's year of pain

21 November 2013

Ukrainian President Viktor Yanukovych reneges on an EU trade deal in favour of closer ties with Russia, provoking protests in the capital which steadily gain in strength.

20-21 February 2014

Clashes at Maidan – the Kiev central square where protesters had set up camp – leave 88 people dead.

A floral tribute to the 88 victims of the clashes at Maidan (Getty) (Getty Images)

22 February

President Yanukovych flees the country. Protest leaders and politicians agree to form a new government and hold elections. Ex-prime minister Yulia Tymoshenko is freed from jail.

27 February

Pro-Russian militias seize government buildings in Crimea.

16 March

In a referendum condemned as illegal by the EU and the US, Crimea votes to secede from Ukraine and join Russia.

24 March

Russia expelled from G8.

6 April

Pro-Russian rebels seize government buildings in Donetsk, Luhansk and Kharkiv.

7 June

Petro Poroshenko is sworn in as Ukraine’s President.

27 June

EU signs association agreement with Ukraine.

17 July

Malaysia Airlines flight MH17 is shot down over eastern Ukraine, killing all 298 people on board. Ukrainian intelligence officials blame a surface-to-air missile fired by rebels.

Victims' belongings at the MH17 crash site (AFP)

22 August

A Russian aid convoy of more than 100 lorries enters eastern Ukraine.

5 September

Ukraine and pro-Russian rebels sign a truce in Minsk.

16 September

Ukraine and EU ratify association agreement.

24 September

Nato reports “significant” Russian troop withdrawal.

26 October

Pro-Western parties win parliamentary elections.

2-3 November

Separatists in eastern Ukraine elect new leaders.

23 January 2015

UN says death toll from conflict exceeds 5,000 and is possibly much higher.

31 January

Major separatist offensive in Donetsk region, following seizure of the airport, causes the collapse of Minsk peace talks.

12 February

Second Minsk agreement signed, following intervention by Angela Merkel and François Hollande.

15-16 February