Hundreds of Ukrainians have gathered outside the parliament in protest over a decision to allow Russia to keep a naval base in the country.
The rally was led by former Prime Minister Yulia Timoshenko, who called on her supporters to block the deal.
It was signed on Wednesday by the Presidents of both countries.
The deal extends Russia's lease of the base for its Black Sea Fleet in the city of Sevastopol for a further 25 years, after the current agreement expires in 2017.
The two leaders also agreed to a 30 per cent discount on Russian gas supplies to Ukraine.
Moscow and Kiev are likely to ratify the deal next week.