Both the European Union and Britain would be "distinctly weaker" if British voters approve leaving the bloc, EU President Donald Tusk said Thursday during a visit to Finland.
"I know it is very difficult for us to be optimistic today," Tusk said referring to next week's referendum in Britain.
"We know the latest polls, it's still 50-50, everything is possible," he told reporters after talks in Helsinki with Finnish Prime Minister Juha Sipila.
The "direct results of a Brexit would be really dangerous for our economy, in the UK and the rest of Europe," Tusk said of possible ramifications of a vote to leave the bloc.
Further, the "political and geopolitical consequences are completely unpredictable," amid strained ties with Russia, for instance.
If British voters vote to leave, Tusk warned of "seven years of political limbo and uncertainty in our relations."
If Britain stays, British Prime Minister David Cameron could negotiate a "new settlement" in "less than one year," he said.
Tusk said Britain has "achieved a position of a key state in the EU, "whose voice is respected, today more than ever before."
"There are so many things we can do together. Leaving now doesn't make any sense," he summed up.
Tusk and Sipila said they believed economic sanctions against Russia would be extended. They were imposed in 2014 over Russia's role in the Ukraine crisis.
Sipila, whose country has seen exports hit by Russian counter sanctions, cited lack of progress "by all parties".