HELSINKI (Reuters) - The European Union should not be split into groups of states that increase their cooperation at different speeds, Finnish Prime Minister Juha Sipila said on Friday.

Finland's Prime Minister Juha Sipila arrives at a European Union leaders summit in Brussels, Belgium, December 15, 2016. REUTERS/Francois Lenoir

He outlined the Nordic euro zone country’s stance as a response to options presented on Wednesday by the EU’s chief executive Jean-Claude Juncker for reforming the bloc to shore up its unity after Britain’s decision to withdraw.

“The main line is that we should all proceed together ... unity is now important, and all members should take part in future decisions as much as possible,” he told Reuters.

Juncker has outlined a possible “multi-speed Europe”, in which some member states could deepen their integration without the whole bloc following suit.

Germany and France have spoken positively of that scenario while some governments, especially in the poorer east, fear it could entrench division to their disadvantage.

Sipila said “formation of different political cores” was not in Finland’s interests. However he singled out common defense as a policy which would need approval from all member states, but that could allow for enhanced co-operation for willing countries.

Sipila said he did not support Juncker’s most dramatic scenarios of the EU scaling back to just policing a common market, or taking a major leap forward in pooling states’ sovereignty.

“Many of the proposed changes would require the re-opening of the EU Treaties. This would mean a multi-year negotiation process with no certainty about its results. The Union cannot afford this,” he said in a column earlier on Friday.

Finland, a net contributor to the bloc’s budget, usually follows Germany’s line on European issues. It took a hard line against bailing out countries during the euro zone debt crisis, and the eurosceptic Finns party is now part of Sipila’s three-party coalition.

Leaders of the 27 states other than Britain will discuss the scenarios outlined by Juncker when they meet to celebrate the bloc’s 60th anniversary in Rome on March 25.