Nick Parsons, of National Australia Bank, said: "It looks as if we are in for another August crisis. The question for Europe is whether things have got better over the past year, and the answer is no. Very little progress has been made."
Markets were also unsettled by reports that the failure of Greece to stick to its austerity program will lead to the IMF cutting off support.
The IMF said it was still working with Athens to get the program back on track, adding that its officials would be arriving in Athens on Tuesday for talks with the coalition government.
On Monday night, Moody's changed its outlook for top-rated Germany, the Netherlands and Luxembourg from stable to negative, warning that they may have to increase support for indebted euro-zone states such as Spain and Italy.
Moody's also cited an increased chance of Greece leaving the euro zone, which "would set off a chain of financial sector shocks ... that policymakers could only contain at a very high cost."
The agency affirmed Finland's AAA rating and stable outlook, but said all four countries were adversely affected by rising uncertainty about the outcome of the euro area debt crisis and the increasing likelihood that greater support would be needed by other euro area countries.
Moody's said the burden of that support would fall most heavily on the euro-zone's top-rated states and Germany, the Netherlands and Luxembourg's "balance sheets are expected to bear the main financial burden of support."
Reports on Monday from Berlin suggested that the mood in Germany is hardening against providing any more assistance to Greece unless fresh austerity measures are both agreed and implemented.
Markets fear that in the absence of bailout cash Greece could be unable to pay its debts by the middle of next month.
Spain's emergency action to ban short-selling led to a late rally in share prices, although analysts warned that the respite was likely to prove temporary.
Spain's borrowing costs soared higher on Monday, taking it closer to a dangerous national bailout as concern switched from the country's ailing banks to its struggling regional governments.
The IBEX index in Spain closed 1.1% down on the day, registering smaller falls than in Germany's DAX (3.2%), France's CAC (2.9%) and Italy's FTSE MIB (2.8%).
In London there was not a single gainer in the FTSE 100, which closed 2.1% lower after a fall of more than 117 points.
New York's Dow Jones Industrial Average was down more than 100 points by close of trading, while fears that Europe's recession-hit economy would drag down global growth led to a drop of $3 a barrel in the price of oil.
Spain's finance minister, Luis de Guindos, was adamant on Monday that his country would not need to ask for more outside help following the decision by last month's European summit to provide €100 billion (£78 billion) for Spain's banks. De Guindos, who will travel to Berlin on Tuesday for talks with Germany's finance minister, Wolfgang Schäuble, said: "Markets are overreacting."
Jonathan Loynes, of Capital Economics, said: "It looks almost certain that Spain will need a sovereign bailout as well as a banking package.
"People were hoping that the euro-zone crisis would die down over the summer and we could all forget about it until September. It doesn't look like that."
Analysts estimate it would cost up to €400 billion to bail out the euro-zone's fourth-largest economy for the next two and a half years.
European commissioner Joaquin Almunia suggested on Monday Spain should try to activate the recently approved bond-buying powers of the euro-zone's rescue funds.
De Guindos is likely to repeat Spanish pleas for pressure to be put on the European Central Bank (ECB) for it to buy Spain's debt and help push down yields. "Spain right now is the breakwater in the current uncertainty surrounding the euro. But this goes beyond Spain," said De Guindos, adding that the country had done its part by approving economic reforms.
ECB President Mario Draghi told Le Monde newspaper on Sunday that buying sovereign bonds was not part of his job.
Spain's economy shrank by 0.4% in the second quarter, compared with 0.3% in the first three months of the year.
A €65 billion austerity package approved earlier this month has not calmed markets and is expected to deepen Spain's double-dip recession even further.
The government now believes recession will extend into next year, with the economy shrinking another half a percent in 2013. Spain's 24% unemployment rate is also thought to be set to remain steady until well into next year. Louise Cooper, of BGC Partners, said the €100 billion package agreed for Spain's banks would not be nearly enough to deal with the country's debt problems. "I think the austerity package is the last thing Spain needs at the moment," she said.
Intellpuke: You can read this article by Guardian Correspondent Giles Tremlett, reporting from Madrid, Spain, and Economics Editor Larry Elliott in context here: www.guardian.co.uk/business/2012/jul/23/spain-markets-eurozone-crisis