Cyprus took the unprecedented step on Monday of closing its banks until Thursday as officials scrambled to renegotiate the terms of a controversial bailout that threatens to force savers to take a €5.8bn (£5bn) hit to their deposits.

Finance ministers from the 17-country eurozone held an emergency video conference call and concluded that small depositors should not be hit as hard as others. They said the Cypriot authorities could stagger the deposit seizures, but remained firm in demanding that the overall sum of money raised remained the same. Cyprus state media said accounts with less than €20,000 may be spared.

The announcement came amid recriminations over the aid package, particularly in Moscow, where a spokesman for Vladimir Putin attacked the plan as "unfair, unprofessional and dangerous".

Thousands of Russians have bank accounts in Cyprus, which has styled itself as a tax haven to attract international deposits into a banking system now at least eight times the size of the island's €17bn economy. Russia hinted that a separate but crucial €2.5bn loan to Cyprus could now be in doubt.

On a day of mounting uncertainty about the punitive conditions of the bailout and the impact on the banking sector:

• Britain temporarily withheld pension payments to more than 12,000 citizens who have retired to Cyprus amid concerns about the safety of the banking system. Up to 60,000 British people are thought to be affected by the seizures.

• A vote on the aid package in the Cyprus parliament was delayed for a second day, until Tuesday, as it became clear that the bailout plan of the newly elected president, Nicos Anastasiades, faced defeat. There were reports on Monday night that he was preparing to tell eurozone ministers that he did not have the votes to get the plan through.

• Stock markets fell – the FTSE 100 lost more than 100 points in early trading – before regaining losses amid speculation that the raid on savings would be scaled down. On the currency market, the euro hit a three-month low.

• European officials raced to defuse criticism that they had imposed the bank levy on a desperate nation.

• The US urged a resolution that was "responsible and fair and ensures financial stability".

Banks in Cyprus had been due to close for a normal holiday giving the authorities an extra 24 hours after the bailout was agreed in the early hours of Saturday, but they will not now reopen until Thursday. Demonstrating their anger at the impact on their savings, hundreds of Cypriots cut short traditional family picnics that mark the first Monday of Orthodox lent and gathered at the Nicosia parliament to protest.

Politicians continued talks behind closed doors on what changes could be made to the proposals before the parliament meets on Tuesday afternoon. Anastasiades said an agreement must be reached if Cyprus was to avoid the collapse of one or all of its banks.

Panicos Demetriades, the governor of Cyprus's central bank, warned parliament: "What would certainly happen is that our two big banks would need to be consolidated. This doesn't mean that they would be completely destroyed. We will aim for this to happen in a completely orderly way."

The terms of the bailout – €10bn of which comes from the eurozone and €7bn from Cyprus through the bank levy and austerity measures – have led to concerns that the €100,000 of savings guaranteed across the EU under an agreement reached in the wake of the 2008 banking crisis is being undermined.

Europe's banking authorities are on high alert for signs of Spanish and Italian savers moving their cash out of national banks for fear of a similar raid. However, officials insisted there was no need for alarm because the Cyprus bailout terms were a one-off that would not be repeated.

In Britain, the Treasury minister Greg Clark appeared to use different language to chancellor George Osborne who had pledged to compensate about 3,000 services personnel stationed in Cyprus when he said they would be compensated for "reasonable losses". Clarke also said pension payments to the Cyprus bank accounts of UK pensioners would be suspended. The pensions were safe, he stressed. "Any UK pensioners in Cyprus can be assured that their future pension payments are being held safely and a normal payment service will resume as soon as the situation in Cyprus becomes clear," Clark said. Of the 18,133 UK pensioners resident in Cyprus, a third use UK bank accounts for their payments and Clark said the others were able "to switch the bank account to which payments are made with immediate effect". Clark said the situation was "uncertain" and subject to change.

The European Central Bank's Jörg Asmussen, who had played a part in negotiating the terms, insisted it was up to Cyprus to alter the way the €5.8bn was raised from bank accounts. The levy was initially set at 6.75% on accounts under €100,000 and 9.9% on any deposit above that sum but this could be altered to 3% on the smaller deposits and up to 15% on deposits above €500,000. In return, savers will be given shares in the banks and, potentially, returns from the country's gas reserves. "The important thing is that the financial contribution of €5.8bn remains," Asmussen said. He also denied responsibility for designing the levy. "I want to emphasise that it wasn't the ECB that pushed for this special structure of the contribution which has now been chosen," he said.

Senior Cypriot officials told the Guardian that Wolfgang Schäuble, the German finance minister, had been the strongest advocate of the savers' tax, but he insisted responsibility lay elsewhere. It had been the Cypriot government, the European commission and the ECB that had pushed for the bank levy, he said.

The terms of the bailout are crucial to Russia as, according to Reuters, nearly half of the €70bn worth of deposits in Cyprus' banks is held by foreigners, and the vast majority are believed to be from Russian officials and oligarchs who have flocked to Cypriot banks seeking the secrecy they are unable to find at home.

Russia's finance minister, Anton Siluanov, warned that Europe's failure to consult with Russia could affect its own decision on maintaining a €2.5bn loan granted to Cyprus last year.

There was speculation that Russia's state-backed energy group Gazprom had offered to inject the cash necessary to prop up the Cypriot banking system in return for licences to exploit potentially vast gas reserves off the coast of the island. But spokesman Sergei Kupriyanov denied that any such approach had been made.

Cyprus has faced criticism that it has become a money-laundering haven for hot Russian cash and this is thought to have motivated the levy on bank accounts.

"Concerns about lax money-laundering regulations have made it politically difficult for a full bailout to be provided, given the worries that rich Russians would be among the main beneficiaries," said Jennifer McKeown, senior European economist at Capital Economics.

Experts warned that even if the levy on deposits below €100,000 was axed entirely, it would not be enough to restore confidence in the bank guarantee system put in place across the eurozone.

"The craziest thing about the Cyprus announcement is the huge potential cost of undermining the spirit of the bank deposit guarantee for what is a small saving in the overall scheme of European finances. Even if policymakers row back from taxing small depositors in Cyprus, the damage has been done," said Tristan Cooper, analyst at the fund managers Fidelity Worldwide.

But Willem Buiter, a former member of the Bank of England's monetary policy committee and now economist at Citigroup, described it as "qualified good news"with some "near-term costs".

Marchel Alexandrovich, at the brokers Jefferies, said: "What is also plainly obvious to anyone observing the current mess is that what should really worry European policymakers is not the €5.6bn in money which is being saved in Cyprus, but the €2,754bn of deposits in the Spanish banking system, of which €182bn comes from deposits outside the euro area."

• This article was amended on 19 March