Ukraine's parliament has warned the regional assembly in Crimea that it faces dissolution unless it cancels a referendum it has called to join the region to Russia.

A resolution, supported by a parliamentary vote, gave the Crimean parliament until Wednesday to call off the referendum, due to take place on Sunday. The Crimean parliament on Tuesday passed a motion stating that it would become independent in the event of a yes vote and then seek to join the Russian Federation, arguing that "the unilateral declaration of independence of part of a state does not violate any international laws". Increasing their isolation from Kiev, the pro-Russian authorities have closed Crimea's airspace to commercial flights.

Also on Tuesday, the acting Ukrainian president, Oleksander Turchinov, announced that a new national guard would be formed in response to Russian attempts to annex Crimea.

Turchinov said mismanagement of the armed forces under the former president, Viktor Yanukovych, meant the Ukrainian military had to be rebuilt "effectively from scratch". The acting defence minister said the country had only 6,000 combat-ready infantry compared with more than 200,000 Russian troops on its eastern borders.

Hopes of a diplomatic solution to the crisis were dealt a blow after the US secretary of state, John Kerry, abandoned a visit to Moscow to discuss the crisis and the US and Russia traded accusations over who was to blame.

As western officials prepared to meet in London on Tuesday to identify Russians who will be subject to asset freezes and travel bans that they hope will persuade Moscow to withdraw its presence from Crimea, the French foreign minister, Laurent Fabius, sought to ratchet up the pressure by warning that sanctions could be imposed as early as this week.

So far, Russia has paid little heed to criticism from the west. Its foreign minister, Sergei Lavrov, said Moscow was preparing counter-proposals to a US plan for a negotiated solution to the crisis. Lavrov said Russia had been prepared to receive Kerry on Monday but the US secretary of state called him on Saturday to postpone his visit.

However, in Washington, state department officials said it was Russia's refusal to discuss the US proposals that was hurting prospects for a negotiated solution, in particular the idea of direct talks between Russian officials and those of the new Ukrainian government.

Spokeswoman Jen Psaki said in a statement: "Secretary Kerry made clear to foreign minister Lavrov that he would welcome further discussions focused on how to de-escalate the crisis in Ukraine if and when we see concrete evidence that Russia is prepared to engage on these proposals."

With little sign that Moscow is prepared to change its position and a potential flashpoint approaching in the shape of Sunday's contentious referendum on whether Crimea should split off and become part of its eastern neighbour, Fabius raised the threat of imminent sanctions in another attempt to get Russia to engage in constructive dialogue.

"If they respond positively [to the proposals], John Kerry will go to Moscow, and then sanctions will not be immediate," he said on France Inter radio. "If they do not respond or if they respond negatively, there will be a series of sanctions that could be taken as early as this week."

The German foreign minister, Frank-Walter Steinmeier, was more cautious, maintaining that the EU would rather avoid confrontation with Russia. He set a deadline of the weekend for "a visible change in Russia's conduct", warning that otherwise measures would be discussed at the European council on Monday.

In his second press conference since he fled to Russia, Yanukovych decried the actions of the new Kiev government and its western allies but shied away from discussing the de facto Russian occupation of Ukraine's Crimean peninsula.

In his only reference to Crimea, Yanukovich said the new regime's policies had "led to the fact that Crimea is seceding", but he did not mention the seizure of the peninsula by unmarked Russian forces at the end of February.

He said he was the legitimate president of Ukraine, arguing he had not fled his post but had simply been "in Kharkov, then in Donetsk, then in Crimea" when opposition forces seized the government. He called the presidential election planned for 25 May "absolutely illegitimate and illegal".

Speaking in Rostov-on-Don, Yanukovych condemned the west for supporting the new government in Kiev, which he said was being taken over by radical nationalists. "I want to ask the sponsors of this dark force in the west: have you gone blind? Have you lost your memory? Have you forgotten what fascism is?" he said.

The self-exiled president appealed to the US Congress, Senate and supreme court to reconsider the aid package being prepared to shore up Ukraine's depleted finances, arguing that US law forbids aid being given to a country that has overthrown a legitimately elected president.

A Ukrainian International Airlines plane was turned back on Tuesday on its way from Kiev to Simferopol, the region's main city, and had to return to the capital.

The captain told passengers the Crimean authorities had closed airspace to all commercial flights, and there had been no flights on Monday either.