Russia's invasion of Ukraine has already, a senior British minister said on Tuesday as Prime Minister Boris Johnson chaired an emergency government response meeting over the Ukraine crisis.

Russian President Vladimir Putin ordered the deployment of troops to two breakaway regions in eastern Ukraine after recognising them as independent on Monday, accelerating a crisis the West fears could unleash a major war.

A Reuters witness saw tanks and other military hardware moving through the separatist-controlled city of Donetsk after Putin formally recognised the breakaway regions and ordered the deployment of Russian forces to "keep the peace".

"You can conclude that the invasion of Ukraine has begun," British Health Secretary Sajid Javid told Sky News. "The Russians, President Putin, has decided to attack the sovereignty of Ukraine and its territorial integrity."

"We will be introducing sanctions as we said we always will," he said.

UK Minister Sajid Javid said sanctions will be announced in a statement to parliament by Johnson.

Russia to be hit with barrage of sanctions, says UK PM Johnson after meeting on Ukraine crisis

Prime Minister Boris Johnson said the UK will hit Russia with a first barrage of economic sanctions, warning that President Vladimir Putin is fixed on a "full-scale invasion of Ukraine".

He was speaking soon after chairing an emergency meeting of the Cabinet Office Briefing Room A (COBRA) on Tuesday in the wake of Putin's decision to recognise two breakaway regions in eastern Ukraine. The UK PM accused Putin of "plainly" violating Ukrainian sovereignty and "the over-running, the subjugation of an independent, sovereign European country.

"He's sent troops in, he's broken international law, he's repudiated the Minsk agreements, and torn up the understanding from Budapest in 1994 that Ukraine's territorial integrity would be respected," said Johnson.

He's completely torn up international law and we will immediately institute a package of economic sanctions, which I think his people would expect. Targeted not just at entities in Donbas, in Luhansk and Donestsk, but in Russia itself targeting Russian economic interests as hard as we can," he said.

Details of the fresh sanctions against Russia are expected to be laid out in the House of Commons soon.

The COBRA meeting follows widespread condemnation of Russia's move, which Johnson termed a violation of international law and an ill omen and very dark time , indicating that things are moving in the wrong direction in the region. Downing Street said the COBRA meeting would discuss the latest developments in Ukraine and coordinate the UK response, including agreeing a "significant package of sanctions to be introduced immediately".

The United Kingdom will be announcing new sanctions on Russia in response to its breach of international law and attack on Ukraine's sovereignty and territorial integrity. There will be severe economic consequences to its actions, UK Ambassador Barbara Woodward told an emergency Security Council meeting on Ukraine.

UK PM Boris Johnson File :Picture

This Council must be united in: calling on Russia to de-escalate immediately; condemning aggression against a sovereign nation, and defending the territorial integrity of Ukraine; calling on Russia to respect its obligations under the Charter to the peaceful resolution of disputes. Russia has brought us to the brink. We urge Russia to step back, she said.

UK Foreign Secretary Liz Truss has confirmed the sanctions, which will use recent legislation to impose restrictions on people and organisations linked to Russia. These will be further enhanced in the event of a feared invasion of Ukraine.

Earlier this month, the UK government passed new legislation that expanded its powers to impose sanctions on those directly linked to Russian actions in Ukraine. The legislation gave the government powers to impose sanctions on Russian businesses and individuals in strategically significant sectors, such as the chemical, defence, extractives, ICT and financial services industries.

Several of the UK's western allies, including the US, France and the European Union, made similar statements condemning Putin's move and promising sanctions.

On Monday evening, Johnson spoke to Ukrainian President Volodymyr Zelensky to outline his grave concern and warn that he believed an invasion was a real possibility in the coming hours and days .

During the phone call, Johnson promised to "explore sending further defensive support to Ukraine" at the request of the country's government, as well as detailing sanctions.

The leaders agreed that the West needed to support Ukraine in the event of an invasion but should continue to pursue a diplomatic solution until the last possible second, Downing Street said.

Regardless of President Putin's actions, the UK would be steadfast in its full support of Ukraine's sovereignty and territorial integrity, the Prime Minister said, it added.

On Monday, Putin's actions were classed as escalation of conflict as he signed a decree recognising the independence of the self-declared people's republics of Donetsk and Luhansk in eastern Ukraine. Russian-backed rebels have been fighting Ukrainian forces in those regions since 2014 and the fears are that military forces could cross Ukraine's borders to occupy the rebel regions recognised by Russia.

Putin claims the troops heading into the two rebel regions will be completing peacekeeping functions. Russia's ambassador to the UN said the country was open to diplomatic solutions but also repeated Putin's accusations blaming Ukraine for escalating aggressions. Ukraine has strongly denied this and declared that it was not afraid and would not yield to Russia.

With inputs from PTI