Russian prime minister Dmitry Medvedev has said the country will honour all its agreements with the European Union and Ukraine, but will trigger "protective measures" if a trade pact between the two comes into force early.
The EUn and Ukraine agreed on Friday to delay the implementation of their free-trade pact until the end of 2015 in a concession to Russia, which is at loggerheads with Ukraine over the conflict in the east of the country.
Mr Medvedev also said on Monday the decision made in Brussels must be given a legal basis.
Mr Medvedev also told members of the country's ruling party, United Russia, that Russia's strength is being tested by sanctions imposed by the West and the country must react in a level-headed way.
"When a series of our partners, if they can be called that, test Russia's strength through sanctions and all kinds of threats, it is important not to succumb to the temptation of so-called easy solutions and to preserve and continue the development of democratic processes in our society, our state," Mr Medvedev said in a televised speech.
On Saturday Ukrainian Prime Minister Arseny Yatseniuk said Russian President Vladimir Putin's goal is to destroy Ukraine as an independent country and to restore the Soviet Union.
Mr Yatseniuk also praised the new wave of economic sanctions imposed on Russia by the EU and US.
He said that they posed a major threat to the Russian economy.
A ceasefire negotiated by envoys from Ukraine, Russia, the separatists and Europe's OSCE security watchdog, has been in place in eastern Ukraine since 5 September.
It is broadly holding despite regular but sporadic violations, especially in key flash points such as Donetsk.
