(QHA) -

Moscow will curtail Ukraine's access to vital Russian markets if Kyiv implements any part of a trade agreement with the European Union, President Vladimir Putin warned in a letter, toughening his stance on a deal at the centre of East-West tensions.

In a letter to Ukrainian President Petro Poroshenko, seen by Reuters 23 September, Putin warned that even changing national legislation to prepare for the EU-Ukraine trade deal, known as the association agreement, would trigger an immediate response from Moscow.

"We still believe that only systemic adjustments of the Association Agreement, which take into account the full range of risks to Russian-Ukrainian economic ties and to the whole Russian economy, will allow (us) to retain existing trade and economic cooperation between the Russian Federation and Ukraine," Putin wrote in the letter, which is dated 17 September.

Putin did not go into detail about possible retaliation, but Russian Prime Minister Dmitry Medvedev said last week he had signed an order to curb Ukrainian exporters' access to Russia. Those measures are yet to take effect.

Substantially raising Russian tariffs could mean €3 billion a year in lost business for Ukraine, which exports mainly steel, coal, chemicals and grains to Russia, EU diplomats say.

QHA