Britain will make it “as painful as possible” for Russia if President Vladimir Putin unleashes an all-out attack on Ukraine, Foreign Secretary Liz Truss has warned.

Ms Truss said the Russian leader appears to be “hell-bent” on invading his neighbour, including potentially an assault on the capital, Kyiv.

She said the Government has further measures “in the locker” which it could activate, after an initial tranche of sanctions announced on Tuesday was widely criticised as being too weak.

Prime Minister Boris Johnson told MPs that three oligarchs linked to the Kremlin and five smaller Russian banks were being targeted in the “first barrage” as the United States and the European Union unveiled similar measures.

The White House, meanwhile, also signalled a halt to diplomatic moves to resolve the crisis, scrapping plans for a potential crisis summit between Mr Putin and President Joe Biden.

It follows Mr Putin’s announcement that Russia would recognise the breakaway “republics” of Donetsk and Luhansk in eastern Ukraine, a move seen by many in the West as a precursor to a full-scale invasion.

Ms Truss said it is still unclear whether Russian troops have crossed into the territories, after Mr Putin said he was authorising the despatch of “peacekeepers” to the area.

“That is, frankly, ambiguous at this stage,” she told Sky News. “We’ve heard from Putin himself that he is sending in troops. We don’t yet have the full evidence that that has taken place.”

She said however that Britain and other Western allies are determined to make it as difficult as possible for Russia if an attack does take place – including through the supply of defensive weaponry to Ukraine.

“I believe that Putin is hell-bent on invading Ukraine,” she told BBC Radio 4’s Today programme.

“This is about inflicting pain on Putin and degrading the Russian economic system over time, targeting people that are close to Putin.

“What we have to do is make it as painful as possible, both by supplying support to the Ukrainian government in terms of defensive weapons, in terms of economic support, and by imposing economic costs.”

Russia is currently estimated to have 150,000 troops massed on the borders around Ukraine, with warplanes and armoured vehicles continuing to deploy in the area.

On Tuesday, Mr Putin said the only way to resolve the crisis is for the government in Kyiv to give up its ambitions to join Nato and to accept the “demilitarisation” of the country.

The list of countries applying sanctions against Moscow has been joined overnight by Japan and Australia.

The most significant measure announced so far is Germany’s decision to cancel certification of the Nord Stream 2 gas pipeline from Russia, seen as a major economic blow to Moscow.

Britain’s sanctions targeted three “very high net wealth individuals” – Gennady Timchenko, Boris Rotenberg and Igor Rotenberg – who are described as “cronies” of the Russian president.

Measures, which include UK asset freezes, a travel ban and prohibition on British individuals and businesses dealing with them, were also tabled against Russian banks Rossiya, IS Bank, General Bank, Promsvyazbank and the Black Sea Bank.

The Government is also drawing up sanctions for members of the Russian Duma and Federation Council, and extending Crimea’s territorial sanctions to the separatist controlled territories in the Donbas.

Shadow foreign secretary David Lammy said the Government needs to act now.

“I think the mood of the entire House of Commons yesterday was that the Government were not being strong enough,” he told BBC Breakfast.

“The Labour Party, of course, but also other parties and backbenchers in the Conservative Party, (are) hugely concerned that we’ve not been strong or hard enough – sending a message to Vladimir Putin that might, at this 11th hour, make him step back.”

Former foreign secretary Jeremy Hunt said the Government needs to take measures that will catch the Kremlin off guard.

“What we have to remember is that Putin has both predicted these sanctions, and indeed further sanctions, and discounted them,” he told the Today programme.

“If we are going to avoid being two steps behind in the diplomatic chess game, we have to do some things that he’s not expecting.”