The warning comes a day before further talks aimed at resolving the 10-month conflict in Ukraine, which shows no signs of abating.

Moscow has hit out at calls for the West to arm Ukraine in the fight against rebels in the east of the country.

A Kremlin spokesman said it would be regarded as an attempt to destabilise the situation – as would the extension of sanctions against Russia.

The warning came ahead of further talks on Wednesday aimed at ending the Ukraine conflict, which has cost more than 5,300 lives since April.

The planned meeting, in the Belarussian capital Minsk, follows last week’s discussions between Russian president Vladimir Putin and Ukrainian leader Petro Poroshenko, led by Germany and France.

Representatives of Ukraine, Russia, separatists and the Organisation for Security and Cooperation in Europe are meeting later to lay the groundwork for Wednesday’s negotiations.

Details of last week’s talks have not been revealed although a French diplomatic official said they included the setting up of a demilitarised zone between Ukraine and Russia, which remained a sticking point.

US President Barack Obama has come under increasing pressure to provide military aid to Ukraine amid claims Russia has been arming the rebels –  claims denied by Moscow.

After meeting German Chancellor Angela Merkel in Washington on Monday, Mr Obama said he had ordered his team to see “whether there are additional things we can do to help Ukraine bolster its defences in the face of Russian aggression”.

Britain has said it will keep its decision not to arm Ukraine under review as it “could not allow” its armed forces to “collapse”.

“It is a national decision of each country in the NATO alliance to decide whether to supply lethal aid to Ukraine,” Foreign Secretary Philip Hammond told MPs.

“The UK is not planning to do so but we reserve the right to keep this position under review.”

He added: “We share a clear understanding that while there is no military solution to this conflict we could not allow the Ukrainian armed forces to collapse.”

A peace deal was reached last Autumn but it has been repeatedly been violated by both sides, and bloodshed has increased significantly in the past two weeks.

On Tuesday rockets hit Ukraine’s military headquarters in the east and a nearby residential area, wounding army personnel and civilians.

Regional police said at least one civilian had been killed and six injured in the strike on the town of Kramatorsk, about 50km (30m) from the front lines.

Officials said the rockets had been fired from the rebel-controlled Horlivka area, some 50km from Kramatorsk.

Earlier, the Ukrainian national guard reportedly launched an offensive against pro-Russian separatists near the strategic south-eastern port city of Mariupol.

The day before, a powerful explosion rocked a chemical plant in the rebel stronghold of Donetsk after shelling by government forces.

Ukraine says fighting has been particularly intense around the town of Debaltseve, a major rail and road junction northeast of Donetsk.

Meanwhile, about 2,000 Russian reconnaissance troops have started month-long exercises in southern Russia, Interfax news agency has reported.

Another news agency, RIA, said more than 600 were in Crimea, which Russia annexed from Ukraine in March.