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Prime minister Dmitry Medvedev said his country would have to respond "asymmetrically" to news that European leaders are planning a wave of fresh sanctions

Russian President Vladimir Putin listens to Russian Prime Minister Dmitry Medvedev, right, at the Novo-Ogaryovo residence outside Moscow  Photo: AP

Hundreds of flights to Asia every week from Britain and other European countries face disruption following a threat by Russia to close its airspace to Western carriers in response to new European Union sanctions over the Ukraine crisis.

The move, which would increase costs for passengers by forcing airlines to revert to more circuitous routes used during the Cold War, was signalled by Dmitry Medvedev, Russia's prime minister, as the EU prepared to publish a detailed list of companies and individuals to face restrictions on their dealings with Europe.

Mr Medvedev told the Vedomosti newspaper: "I hoped that our partners would be smarter. If there are sanctions related to energy, or further limits for our financial sector, we will have to respond asymmetrically.

"We proceed from the fact that we have friendly relations with our partners and that is why the sky over Russia is open for flights. But if they put limits on us we will have to respond."

Today a shaky ceasefire between Ukrainian government forces and pro-Russian separatists in eastern Ukraine extended into a third day, despite isolated outbreaks of fighting and exchanges of artillery fire.

On a visit to the region, Petro Poroshenko, Ukraine's president, said that there was no military solution to the crisis and that the Kiev government would instead focus on "winning the peace".

But in a signal that Kiev is determined not to cede any further ground to the rebels, Mr Poroshenko ordered reinforcement of the embattled city of Mariupol, telling steelworkers there that it "is, was, and will be part of Ukraine".

"I have ordered [the military] to secure the defence of Mariupol with howitzers, multiple rocket launchers, tanks, anti-tank weapons and air cover," he said during a visit to one of the city's two vast steel factories. Despite the ceasefire, the EU was expected late last night or sometime today to put Russia's main oil producers and pipeline operators Rosneft, Transneft and Gazprom Neft on its list of state-owned firms to be prevented from raising capital or borrowing on European markets.

Aviation industry sources said that cutting off Russian airspace would mean longer flights to South East Asia in particular, and higher fares as airlines pass on the extra fuel cost to passengers.

"It would clearly mean rerouting some flights," said an expert on the German aviation industry, where the country's major airline, Lufthansa, is likely to be hit hardest. "It would add to flight times and then there is the question of what would happen to flights into Russia – it would end connectivity. It would be one step before war to cut off all connectivity and over-flying."

A British aviation source said: "At the end of the day, we have been there before when Soviet airspace was shut."

American airlines would be more easily able to devise flight plans that skirt the region than their European counterparts, industry sources said.

Of the 1,600 flights operated by 39 airlines east of the Urals in the week between July 29 and Aug 6, about half were operated by EU carriers and 469 were shared by Lufthansa and Air France/KLM, according to data from Flightradar24, an aircraft-tracking service.

British Airways had 93 flights across Siberia that week, including from London to Tokyo, Seoul and Hong Kong, Bloomberg reported.

Mr Medvedev suggested it was not too late for the West to avoid an airspace ban that would force "many airlines" to go bankrupt. "That is a bad story. We just want our partners to realise it at some point," he said. "Sanctions certainly don't help bring peace in Ukraine. They hit wide off the mark and an absolute majority of politicians realise that."

Brussels says it could review the sanctions if Russia stops backing the rebels and the ceasefire in Ukraine holds.