BUDAPEST—Hungary defended its economic management after a second credit-rating firm stripped the country of its investment-grade status, a move that could further hamper growth.

"Few can see at present the progress we have made," Gyorgy Matolcsy, the economy minister, said Thursday, adding that the government is laying the groundwork for faster economic growth. "We have been receiving slaps in the face from here and there, from rating agencies and some friends alike."

Announcing its decision to lower Hungary to junk status, Standard & Poor's Ratings Services said late Wednesday that the economy was suffering from policies that lack predictability and credibility.

The governing center-right Fidesz Party has raised questions at home and abroad about its dedication to a market economy. The most recent catalyst for criticism was a bill it introduced last week that was widely believed to infringe on the central bank's independence.

Moody's Investors Service already downgraded Hungary to junk status last month and analysts expect Fitch Ratings to follow suit early next year.