Russian Prime Minister Dmitry Medvedev said in an interview broadcast by Russian TV that it would adopt a tough position if Ukraine decided not to pay off debts owed by its previous government.
"If it is actually formulated in this way this would undoubtedly be a default of Ukraine ... We would adopt as tough a position as possible in this case and defend our national interests," Medvedev told the Vesti on Saturday programme on state TV channel Rossiya.
Medvedev also said his government had an interest in seeing a predictable rate for the rouble, but he defended the central bank's policy of allowing the rouble to float, saying it was "optimal" to achieve a balance in the forex market between supply and demand.
The Ministry of Defence has said at no time was there a perceived threat from Russia planes that were tracked flying towards UK airspace.
The two Russian Bear military aircraft were escorted by RAF Typhoon fighters after they were scrambled when the initially unidentified aircraft were spotted flying North of Scotland.
It is the latest of similar incidents involving Russian military aircraft flying close to UK airspace in recent months.
RAF Typhoon fighter jets have intercepted Russian aircraft that were tracked flying towards UK airspace earlier today.
The jets were scrambled from RAF Lossiemouth and escorted the Russia Bear aircraft until they were out of the UK area of interest, an RAF spokesperson said.
"The aircraft were identified as Russian Bear aircraft which were escorted by the RAF Typhoon fighters until they were out of the UK area of interest.
"At no time did the Russian military aircraft cross into UK sovereign airspace", the spokesperson added.
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US Secretary of State John Kerry has met with Russia's President in a bid to end the freeze in relations since the Ukraine crisis beganRead the full story ›
US Secretary of State John Kerry is set to meet with Russian President Vladimir Putin in Russia today to discuss the ongoing conflicts in Ukraine and Syria.
Kerry is reportedly planning to try to gauge Putin's willingness to push pro-Russia separatists in Ukraine to comply with the current fragile ceasefire and also to try and establish how supportive Russia are towards Syrian President Bashar Assad.
The US State department have described Kerry's trip to Sochi as part of an "ongoing effort to maintain direct lines of communication with senior Russian officials".
Kerry is also expected to lay a wreath at a World War II memorial during his visit before departing for a Nato meeting in Turkey later in the day.
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Members of a nationalistic Russian bikers club have laid a wreath at a monument to the Russian soldiers who liberated Vienna from the Nazis.
The pro-Kremlin Night Wolves are on a ride commemorating the Russian and Allied defeat of Nazi Germany 70 years ago in the Second World War.
They started in Moscow and are hoping to end in Berlin on May 9.
Some EU officials have expressed criticism of their plans and Poland denied them entry, reflecting strains between Warsaw and Moscow over Russia's role in the Ukraine conflict.
Maya Plisetskaya, a ballerina regarded as one of the greatest of the 20th Century, has died aged 89.
Bolshoi director Vladimir Urin told the state news agency Tass that Plisetskaya died in Germany of a heart attack on Saturday.
President Vladimir Putin issued a message of condolence and tributes came from across the dance world.
Plisetskaya was renowned for intense performances that contrasted with the ethereal style of many other dancers, especially in Tchaikovsky's Swan Lake.
Plisetskaya joined the Bolshoi troupe in 1943 at the age of 18 and stayed until 1990 when she left amid disputes with its director.
However, she returned to its stage for gala appearances, including a 75th birthday performance in 2000.
She is survived by her husband, composer Rodion Shchedrin.