HELSINKI—Finland thinks the European Union should wait in implementing its new economic sanctions against Russia, Finland's prime minister said Monday.

The EU launched on Monday the process to adopt formally a set of new measures that will slightly stiffen the EU's response to Russia for its role in the Ukraine crisis.

The new sanctions were adopted by the EU members including Finland on Monday, but the actual timing for their implementation was left to be decided later, Finland's Prime Minister Alexander Stubb told Finnish media at a press briefing in Helsinki shortly after 1900 local time (1600 GMT).

"Finland in general isn't of the opinion that now is the right time [for the sanctions]," Mr. Stubb said, adding that EU diplomats were negotiating in Brussels on Monday night over when the sanctions would actually be put into force.

To come into force the sanctions have to be entered in the EU's official journal, "but there are still discussions at which stage [the sanctions] will be published in the official journal," Mr. Stubb said.