The president of the European Central Bank gave a guardedly upbeat assessment of the situation in the euro zone Thursday, saying that troubled countries had made “significant progress” remaking their economies and that the banking system was healthier.


“So, not bad,” Mario Draghi said, with an air of distinct satisfaction, at a press conference in the Slovenian capital of Ljubljana following a meeting of the bank’s governing council.


But, perhaps wary of seeming too optimistic and encouraging complacency by elected officials, he added that the state of the euro zone remained tenuous. Early this year, Mr. Draghi also called a turning point in the crisis, only to see tensions return with a vengeance later on.


After a period of intense activity to calm the euro zone crisis, the E.C.B. had not been expected to announce major new policy actions Thursday. And, as expected, the bank left its benchmark interest rate at a record-low 0.75 percent.


Instead, the focus has been on elected leaders, and particularly whether Spain will meet conditions for the E.C.B. to start buying its bonds as a way of restarting bank lending in the country.


Mr. Draghi asserted that the E.C.B.’s promise to buy bonds in so-called Outright Monetary Transactions had “helped to alleviate tensions” in the markets.


He added that the bond purchases, once they begin, “will enable us to provide, under appropriate conditions, a fully effective backstop to avoid destructive scenarios with potentially severe challenges for price stability in the euro area.”


But he also called on governments to do their part to continue to make progress on overhauls of national economies and the structure of the euro zone.


And he warned that, if the E.C.B. began buying bonds to help a euro zone country hold down borrowing costs, the bank would cut off aid if countries failed to meet agreed conditions.


Last month, Mr. Draghi set out the terms for the central bank to begin buying euro zone government bonds. One of the conditions was that countries must request help from the euro zone bailout fund. Until Spain takes that step, the E.C.B. is not likely to take action.


The E.C.B. promise last month to intervene in bond markets, as well as Mr. Draghi’s vow to do “whatever it takes” to preserve the euro, has calmed tensions considerably. But market interest rates for Spanish bonds have been creeping higher in recent weeks as Prime Minister Mariano Rajoy delays asking for relief, a move which would require him to accept restrictions on how he manages the economy.


On Thursday, the Spanish Treasury successfully auctioned €4 billion of debt, the maximum amount that it had aimed to sell, amid strong demand and paying lower interest rates than when it last sold such bonds.


Analysts cautioned, however, into reading too much into the positive result.


Nicholas Spiro, managing director of Spiro Sovereign Strategy, a research concern, wrote Thursday in a note that investors were “taking an overly optimistic view” of the eventual effectiveness of the E.C.B. bond-buying program.


“Spain’s debt market is currently in a state of limbo,” he wrote. “It is being propped up by an E.C.B.-backed bond-buying scheme that has yet to be put into practice.”


In his remarks Thursday, Mr. Draghi presented a somewhat rosier picture of the situation in the euro zone, saying that “significant progress” has been made in countries like Spain and Portugal. He also noted that weaker banks in the euro zone had bolstered their capital cushions.


“When I said there has been significant progress, I included the repairing of the banking system,” Mr. Draghi said. “The capitalization gap that was pretty wide a couple of years ago has been significantly reduced.”


Mr. Draghi ticked off a number of signs that the crisis has eased, including inflows of bank deposits to Italy and a rise in bond sales by banks and corporations, which should help investment and lending. He also said that Spanish banks had become less dependent on lending from the E.C.B., a possible sign they are able to raise funds on markets.


But he added, “We also have to express a note of caution. Volatility is still relatively high. And governments will have to persevere on their reform action.”


Mr. Draghi also reiterated his view, which some euro countries have questioned, that the central bank’s actions to shore up the euro fall squarely within its purview.


“Let me repeat again what I have said in past months,” he said. “We are strictly within our mandate to provide price stability over the medium term, we act independently in determining monetary policy, and the euro is irreversible.”


From the E.C.B.’s point of view, there would have been little point in further cutting the main interest rate from 0.75 percent. Rates are already probably too low for stronger countries like Germany, while the official rate is no longer having much effect on borrowing costs for business and consumers in the troubled countries.


In addition, a rate cut now would have left the E.C.B. with few policy options if the situation in the euro zone deteriorates further.


“While a rate cut could easily be justified by the economic outlook,” analysts at ING wrote in a note Wednesday, “we think that the E.C.B. is not yet willing to fire this very last shot.”


Raphael Minder contributed reporting from Madrid.