The European Central Bank continued its efforts hold down the interest rates paid by highly indebted governments in the region, buying $20 billion worth of government bonds over the past week, according to newly released figures.

Analysts say the bulk of the money was likely spent on bonds from Italy and Spain, two large economies where rising interest rates earlier this month raised fears about whether they could continue to pay their bills.

European countries, already strained by emergency bailouts for Greece, Ireland and Portugal, would be hard-pressed if either Italy and Spain needed to be rescued. Bailouts for either of those nations would tax the financial tools available, possibly cause crippling losses for banks throughout the area, and be politically difficult to engineer.

As European officials struggle for a durable solution to their problems, the ECB has become the “investor of last resort,” keeping rates at reasonable levels for Italy and Spain, ING analyst Paolo Pizzoli wrote after the ECB disclosed its bond-buying totals for the past week.

The ECB does not break down its purchases on a country-by-country basis. But Pizzoli estimated that the purchases — following a record $30 billion bought the week before — have kept Spanish and Italian borrowing costs down by a full percentage point after they spiked toward levels that would have put the countries at risk. “The market impact of recent bond purchases has been substantial,” he said.

European stock markets began the week up on a largely positive note. The Stoxx 50 index of euro-zone blue-chip companies was up more than 1 percent.

But analysts and officials expect several tense weeks while national legislatures in Europe debate measures recently approved by their leaders that would expand common efforts addressing the economic crisis and approve an enlarged bailout package for Greece.

Approval is not a foregone conclusion. The measures are controversial in Germany and the Netherlands. Finland has put the Greek bailout in doubt by demanding that Greece post millions of dollars in collateral for the Finnish share of an emergency loan. The Dutch government has called the deal between Greece and Finland illegal, and at least three other European countries are also insisting that they get collateral for their shares of the Greek loan.

Moody’s Investor Services warned that the dispute over the Finnish collateral demand could scuttle the bailout, causing Greece to default, according to Reuters.

Until those measures are approved, analysts expect the ECB to continue adding to its holdings of government debt, which amounts to roughly $150 billion. But analysts say it may take much more — perhaps in excess of $1 trillion — to fully shield Spain and Italy from a debilitating rise in interest rates. Italy on its own has about $2 trillion in outstanding bonds.

The bank’s bond program is taking place amid a broader debate about how to solve the region’s financial problems. One idea under wide discussion is the creation of a “eurobond” that would be backed by all 17 nations that use the currency — effectively using the borrowing power of stronger nations such as Germany to raise money for Greece or Italy.

In weekend interviews, German Chancellor Angela Merkel repeated her staunch opposition to the idea. She told German television that eurobonds would only make sense in the distant future, and would destabilize Europe if adopted before the economies of the 17 euro-zone nations were ready.

“At this time — we’re in a dramatic crisis — eurobonds are precisely the wrong answer,” Merkel said in the interview, according to Bloomberg News. “They lead us into a debt union, not a stability union. Each country has to take its own steps to reduce its debt.”