By Toby Sterling and Anthony Deutsch
AMSTERDAM (Reuters) - The outcome of a non-binding Dutch referendum on broader European Union ties with Ukraine was too close to call on Wednesday, with a vital turnout threshold hanging in the balance, exit polls showed.
The vote, launched by anti-EU forces, is seen as test of the strength of eurosceptics on the continent just three months before Britain votes on whether to stay in the European Union.
Although it is non-binding, it will be considered as an advisory referendum by the government if turnout reaches 30 percent. Otherwise it will be considered null and void and need not be taken into consideration by the government.
The pollster Ipsos put total turnout at 32 percent - above the threshold - in a revised exit poll after an initial survey showed turnout at 29 per cent. The margin of error was 3 percent. The referendum's validity was still unclear, it said.
In a rebuke for the government, which campaigned in favor of the EU-Ukraine association agreement, roughly 64 percent voted "No" and 36 percent said "Yes", according to the initial exit poll.
The political, trade and defense treaty is already provisionally in place but has to be ratified by all 28 European Union member states for every part of it to have full legal force. The Netherlands is the only country that has not done so.
Eurosceptics had presented the referendum as a rare opportunity for their countrymen to cast a vote against the EU and the way it is run - including its open immigration policies.
In the run-up to the referendum - the first since a 2015 law made it possible to force through plebiscites by gathering 300,000 signatures on the Internet - polls had a "No" vote against the agreement leading by a wide margin.
The turnout, far lower than in national or local elections, reflected many voters' puzzlement at being asked to vote on such an abstruse topic.
"I think the people who asked for this referendum have made a huge commotion," said Trudy, a "Yes" voter in central Amsterdam. "It's nonsense, which cost lots of money, and it's about something nobody understands."
Geert Wilders, leader of the eurosceptic Freedom Party, urged voters to send a message to Europe by saying "No".
"I think many Dutchmen are fed up with more European Union and this treaty with Ukraine that is not in the interests of the Dutch people," he told reporters.
"I hope that later, both in the United Kingdom and elsewhere in Europe, other countries will follow."
A clear vote against the treaty in the run-up to Britain's June 23 referendum on whether to quit the EU could escalate into a domestic or even a Europe-wide political crisis.
Dutch leaders say voting against the treaty would also hand a symbolic victory to Russian President Vladimir Putin.
Pro-Russian separatists in Ukraine are accused of bringing down an airliner in 2014 with the loss of almost 200 Dutch lives.
It is unclear if anti-Russian sentiment swayed voters nearly two years on but increasing resentment among the Dutch at the consequences of the EU's open-border policies has propelled Wilders -- who openly opposes Muslim immigration -- to the top of public opinion polls.
The ballot also taps into a more deep-seated anti-establishment sentiment highlighted by a resounding rejection in 2005 of a European Union constitution, also in a referendum.
In parliament, Prime Minister Mark Rutte's conservative VVD party has said it would ignore a narrow "No" vote, while junior coalition partner Labour has said it would honor it, setting the stage for a split.
But ignoring a clear "No" would be risky for Rutte's already unpopular government -- which has lost further ground over Europe's refugee debate -- ahead of national elections scheduled for no later than March 2017.
(Additional reporting by Thomas Escritt and Svebor Kranjc in Amsterdam, Gabriela Baczynska in Brussels, Dmitry Solovyov in Moscow.; Editing by Angus MacSwan)