By MARTIN VAUGHAN SINGAPORE—Several Asian central banks stepped into the foreign-exchange market Thursday to temper a sell-off in their currencies, aiming to keep them from weakening too rapidly as strains from the euro zone's debt crisis are felt across the region. Central banks in Indonesia, Malaysia, the Philippines and South Korea were spotted selling dollars in relatively small amounts, as their currencies came under pressure from a region-wide move by investors to pare risky bets. Asian currencies have turned lower against the dollar in the second half of this year as euro-zone stresses have intensified. That followed a long period of steady appreciation after the 2008 financial crisis. Most central banks have plenty of firepower to defend their currencies, as they have built up large dollar reserves thanks to current account surpluses and past efforts to slow the rise of their currencies. And Asian economies for the most part are solid, making a severe rout in their currencies unlikely. "These central banks can make the point that the declines in their currencies are not necessarily justified by fundamentals," said Olivier Desbarres, head of FX strategy for Asia Pacific excluding Japan at Barclays Capital. "I don't think any of them are necessarily trying to draw a line in the sand. But they do want to smooth the intra-day volatility by showing their hand in the market," he added. In the past week, the Korean won has lost around 2.7% against the dollar while the Philippine peso has shed around 2%. But the declines haven't been uniform across Asia. The Taiwan dollar has fallen by less than 1% over that period while the Chinese yuan and Hong Kong dollar have been more or less flat. That may have provided some impetus to the authorities, who don't like their currencies to get too far out of line with regional peers. Currency dealers said the dollar has muscled higher in response to renewed concerns about stability in the euro zone, after markets were unimpressed with European leaders' efforts to get the sovereign debt crisis there under control. The euro's break below $1.3000 Wednesday—a long-time support level—helped trigger a sell-off in commodities and put holders of riskier assets even more on edge. Inflation worries may also be part of what's driving Asian central banks to intervene. Inflation has plagued much of the region over the past year, thought it has eased somewhat in some countries. But authorities remain vigilant. Weaker currencies would increase prices of imported goods, stoking broader price pressures. Traders in Seoul said the Bank of Korea may have sold around $300 million to support the won, at roughly 1,163 won. Bank Indonesia may have sold around $20 million at 9,150 rupiah, traders said. Bank Negara Malaysia sold dollars at around 3.1970 ringgit, while Bangko Sentral ng Pilipinas sold at around 44.25-44.33 pesos, traders said. One central bank that has remained on the sidelines despite mounting pressure to step in is the Reserve Bank of India. The rupee continued its free fall against the dollar Thursday, as the dollar touched a new record high of 54.22 rupiah. The RBI has promised to make a "definitive statement" on the rupee at its mid-quarter monetary policy review Friday. --Andreas Ismar in Jakarta, Ankur Relia in Kuala Lumpur, Rhea Sandique-Carlos in Manila, and Jieun Shin in Seoul contributed to this article.

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