Russia has “no justification whatsoever” for its aggression towards Ukraine, Liz Truss has warned, ahead of an “absolutely critical” week for Europe’s peace and security.

The Foreign Secretary, who is planning to visit Kiev later this month, told MPs Russia’s president Vladimir Putin has been “peddling” the “false narrative” of a security threat in the region which the Kremlin is responding to.

She insisted any Russian military incursion into Ukraine would be a “massive strategic mistake” and would “come at a severe cost”, including the prospect of “co-ordinated sanctions” to hit the country’s interests and economy.

Europe must also reduce its dependence on Russian gas, the Foreign Secretary said.

Russian military build-up on Ukraine’s border has raised concerns over the intentions of Mr Putin towards the former Soviet country.

Ms Truss, making a statement in the House of Commons, said the UK’s commitment to Ukraine is “unwavering” and it joins its allies in defending “democracy at the frontier of freedom in eastern Europe and around the world”.

She added: “We will not accept the campaign Russia is waging to subvert its democratic neighbours. It is accompanied by baseless rhetoric and disinformation.

“They have falsely cast Ukraine as a threat to justify their aggressive stance. They falsely accuse Nato of provocation; this could not be further from the truth.

“Russia is the aggressor here. They have massed a huge number of troops along the Ukrainian border and in illegally annexed Crimea.

“There is no justification whatsoever for Russia’s bellicose stance towards Ukraine. It is unprovoked and it is part of a wider pattern of behaviour by the Kremlin, reliant on disinformation and mistrust to seek to gain an upper hand.”

After outlining Russian actions elsewhere in the world, Ms Truss said: “I urge Russia to end its malign activity and to stick to what has been agreed.”

Ms Truss added: “This next week will be absolutely critical for peace and security in Europe.

“Tomorrow, I will join an extraordinary meeting of Nato foreign ministers. The US-Russia dialogue begins on Sunday, followed by the Nato-Russia Council on Wednesday, and the OSCE (Organisation for Security and Co-operation in Europe) Permanent Council on Thursday.

“We will be in talks on the basis of freedom, democracy and the rule of law. It’s vital that Nato is united in pushing back against Russia’s threatening behaviour, and together we must hold Russia to its longstanding obligations.

“There can be no rewards for aggression.

“We are reaching a crucial moment. The only way forward is for Russia to de-escalate and pursue a path of diplomacy.

“We will continue to stand together with our allies, steadfast in support of Ukraine and its future as a free and sovereign democracy.”

The UK is helping Ukraine “strengthen its defences with joint exercises, maritime support, and by training over 20,000 members of its army, with more to come”, Ms Truss said.

She added: “Europe must reduce its dependence on Russian gas. Britain remains opposed to Nord Stream 2 (a new pipeline running from Russia to Europe across the Baltic Sea) and I’m working with allies and partners to highlight the strategic risks of this project.”

For Labour, shadow foreign secretary David Lammy said Russia’s actions are “driving this dangerous escalation of tensions”.

He told MPs: “It is right that this whole House sends a clear and unified message today, that we fully support Ukraine’s sovereignty and territorial integrity and that Russian actions to further undermine this will be met with severe consequences.

“We must be crystal clear in our commitment to Nato and to the security of our allies. That commitment must be unshakable. It is also right that we support dialogue to achieve de-escalation, consistent with the security of our Nato allies and the integrity of Ukraine.”

Tom Tugendhat, Conservative chairman of the Foreign Affairs Select Committee, insisted Nato is a “free association of free people defending freedom”.

Ms Truss said it is a “sovereign decision for Nato and relevant applicant states as to whether they join Nato” and “not a decision for Russia”.

Conservative former defence minister Tobias Ellwood said he does not believe the West has a coherent strategy to deal with Russia’s aggression.

He asked: “With the West looking ever timid, ever divided and ever risk-adverse, with the United States looking ever distracted because of domestic issues, and Nato bruised after its retreat from Afghanistan, has there ever been a better time for Russia to invade Ukraine than in the forthcoming new year of the Orthodox calendar?”