President Vladimir Putin of Russia says a Ukraine-EU free trade deal would pose a "big threat" to Russia's economy.
He said Russia could be flooded with European goods virtually without tariffs because of an existing free-trade regime between Kiev and Moscow.
Kiev last week delayed the signing of the deal, prompting the EU to accuse Moscow of pressuring Ukraine.
The move triggered pro-EU protests in Ukraine in Kiev and other cities. But President Viktor Yanukovych said he wanted for better terms Ukraine in the deal.
The BBC reports demonstrators have pledged to continue their rallies until 29 November, when Ukraine originally planned to sign the free trade and association agreement.
During a visit to Italy, President Putin said Russia's economy would be hit if European goods were allowed to transit through Ukraine tariff-free.
He said Russia's agriculture, car and aviation industries would suffer as a result and there could be a jump in unemployment.
"We are not ready to open our gates to European goods," he said.
Mr Putin urged EU officials to refrain from "sharp words" on the issue. Referring to them as "our friends in Brussels", he said: "Do we have to choke entire sectors of our economy for them to like us?"
On Monday, European Council President Herman Van Rompuy and European Commission President Jose Manuel Barroso said they strongly disapproved of Russia's "position and actions".
But the BBC reports Mr Putin denies pressuring Ukraine, accusing instead the EU of "blackmailing" Ukraine to sign the treaties.
