Pedestrians walk along a board listing foreign currency rates against the Russian ruble outside an exchange office in central Moscow on December 12, 2014 © AFP/File Kirill Kudryavtsev Moscow (AFP) - When Olga Savelyeva took out a $226,000 mortgage to buy a small apartment on the outskirts of Moscow in 2008, she could never have imagined that the ruble would lose more than half its value in a few short years.

But Savelyeva's $2,090 monthly instalments have skyrocketed in ruble terms due to the Russian currency's dive against the dollar. The resulting jump in monthly payments from 49,000 to 115,000 rubles now devours most of her family's income.

The 30-year-old mother of a young daughter and her husband have tried to honour their repayment commitments but despite their best efforts, December's instalment was $400 short.

"We're left with 3,000 rubles ($56) this month," Savelyeva told AFP.

"We won't be able to make the January payment in full... "We also have other obligations," she added, referring to her retired mother and cancer-stricken father.

Savelyeva is one of tens of thousands of Russians who took on lower-interest foreign currency-denominated mortgages in the years before the financial crisis and now struggle with repayments as the ruble's value shrinks.

Russia's central bank says that as of November 1, foreign exchange mortgage debt totalled 120.5 billion rubles ($2.28 billion).

According to the state-run Agency for Housing Mortgage Lending, those loans represent 3.3 percent of the total volume of outstanding mortgage debt.

Critics say the government is deliberately downplaying the scope of the problem and claim some 100,000 to 150,000 people are likely affected.

Hundreds of Russia's hard-currency mortgage holders have created a social media group, attracting members from Yekaterinburg in the Urals to the exclave of Kaliningrad on the Baltic Sea.

In a letter to central bank chief Elvira Nabiullina, the group threatened a "powerful social explosion" if assistance isn't provided.

Some 100 homeowners picketed the central bank this month and around 500 people plan to take to the streets this week, the first significant protests over the collapse of Russia's currency -- down some 40 percent against the greenback this year.

- 'Left alone with misfortune' -

With Russia's mortgage industry still in its formative phase, taking out a loan to buy a home is considered risky business.

Even before the crisis, interest rates of 10 to 12 percent on foreign currency loans -- and 12 to 14 percent on ruble-denominated mortgages -- mean many Russians will wind up paying double to triple the principal borrowed on 15- to 20-year loans.

The group of foreign currency mortgage holders says Russia's financial crisis, exacerbated by falling oil prices and Western sanctions over Ukraine, has transformed their loans into "financial slavery".

To make matters worse, interest rates are expected to rise further still in the wake of the central bank's decision this month to hike its key rate to 17 from 10.5 percent to prop up the ruble.

"Why have ordinary borrowers been left alone with their misfortune?" asked members of the social media group in their letter to the central bank.

They said some of them have "ended up out on the streets" and warned they would be ready to go on hunger strike if no solutions were found.

A representative of the Bank of Russia said it had repeatedly warned clients of the risks associated with dollar-denominated mortgages.

The bank added that "a restructuring of such loans, including converting them into rubles at a reasonable exchange rate, would be in the interests of both borrowers and banks".

Zoya Kuliyeva, who borrowed $120,000 to buy a Soviet-era apartment in Moscow in 2008, said banks have so far refused to come up with an acceptable solution.

The bank has offered to extend her loan until she turns 70. "It means my children and grandchildren will be paying it off," Kuliyeva, chief accountant at a Russian firm, told AFP.

- 'State help needed' -

Economist Yevgeny Gontmakher said the collapse of the ruble was a huge blow to Russia's middle class, which includes many holders of foreign-currency loans.

"It's a catastrophe for them," said Gontmakher, deputy director of the Institute of World Economy and International Relations of the Russian Academy of Sciences.

The government, he added, would likely pass the buck by putting pressure on the banks, which are already struggling with a liquidity squeeze.

This year Hungary faced a similar scenario, with banks forced to convert foreign currency debt into forints to bail out hundreds of thousands of borrowers.

Russian lawmakers this month passed a personal bankruptcy law that will come into force next July.

A legislator from A Just Russia party, Andrei Krutov, suggested that foreign currency-denominated loans be banned altogether.

Krutov also said the state should bail out holders of those mortgages by allowing them to pay off loans at pre-crisis exchange rates.

"They won't be able to get by without state support," he told AFP, adding that he was preparing legislative initiatives to that end.

But Kuliyeva said such assurances offered little consolation.

"I am just trying not to follow the dollar exchange rate," she said. "It's very scary, it's depressing."