A "No" vote in the Greek referendum on bailout terms would not provide Greece with an easy way out of its economic crisis, the head of the grouping of eurozone finance ministers has said.
Jeroen Dijsselbloem's comments came after Greek Prime Minister Alexis Tsipras told Greeks a "No" vote would lead to a "better agreement".
But Mr Dijsselbloem insisted that suggestion was "simply wrong".
Long queues of pensioners have formed outside Greek banks for a second day.
Follow the latest updates
Meanwhile, the International Monetary Fund (IMF) has issued a report saying that the embattled country needs an extra 50bn euros ($55bn) over the next three years to stabilise its finances under the existing, disputed creditor plans.
In the report, the IMF cuts its forecast for Greek economic growth this year from 2.5% to zero, saying that changes in Greek policies and its financial outlook since early 2015 "have resulted in a substantial increase in financing needs".
At the scene: Joe Miller, BBC News, Athens
Greece's banks have now been closed to all but pensioners for four days, and Athenians have settled into a crisis routine.
At the stroke of midnight, queues form at cash machines as locals scramble to obtain their daily €60 ration.
Neighbours confer over which ATMs are still dispensing €20 bills - those with other denominations can only pay out €50 per day.
But despite the posters that adorn every tree and lamppost calling for "everyone to take to the streets", the large protests of the past few days have largely died down.
In the radical left Exarcheia neighbourhood, exhausted young anarchists lounge outside bars and cafes, and let the banners hanging across the central square speak for them.
"No to EU and IMF terrorism," reads one.
"€ + Germany = oppression," reads another.
Did Tsipras change course?
Splits threaten Syriza coalition
Is Greece's exit from the euro inevitable?
Mr Dijsselbloem, who is also the Dutch finance minister, told a parliamentary committee in the Netherlands that a rejection of the current bailout terms by Greek voters in Sunday's hastily arranged referendum would make it hard for the two sides to bridge "fundamental differences".
It would place both Greece and Europe in a "very difficult position", he said.
"The Greek government is rejecting everything with the suggestion that if you vote 'No' you will get a better or less tough, or more friendly package. That suggestion is simply wrong," he added.
Greece's banks stayed shut this week after emergency funding from the European Central Bank (ECB) was frozen, though some branches have reopened to allow pensioners - many of whom do not use bank cards - a one-off weekly withdrawal of up to €120.
Withdrawals from cash machines are capped at just €60 a day.
Local media are reporting growing pressure on the economy, with businesses halting production because they are unable to pay suppliers, and some shops considering giving unpaid leave to staff.
Now that any deal before the referendum has been ruled out by European leaders, both sides are hoping the argument is finally settled by the ballot box.
Greece's left-wing Syriza government, elected on an anti-austerity platform, has been in deadlock with its creditors for months over the terms of a third bailout.
Last weekend, it took the unilateral decision to hold a vote on those terms.
On Tuesday, the previous eurozone bailout expired, depriving Greece of access to billions of euros in funds, and Athens missed a €1.5bn repayment to the IMF.