"Our debt is clean, we will not have to ask for help," Elena Salgado said in an interview with newspaper Cinco Dias, adding she believed the downgrade was unjustified.
"Frankly, I think the concrete facts do not support this decision," she said.
Spain, which has pledged to reduce its deficit of 11.2 per cent last year to three per cent by 2013, announced a series of austerity measures on Friday to help meet the target.
The government said it would save $21m annually by cutting the number of public companies and societies by 29 to 77 and by eliminating 32 posts of senior officials in government ministries.
The number of state-owned enterprises will be reduced through mergers and 14 closures, said Maria Teresa Fernandez de la Vega, the deputy prime minister.
The cuts came as unemployment figures released on Friday showed the severity of the situation in Spain, with the jobless rate passing 20 per cent for the first time in 13 years.
The National Statistics Institute said the rate rose 1.22 percentage points in the first quarter to 20.05 per cent.
Greece's 'red line'
Fears arose on Thursday that the Greek debt crisis would spark a domino effect in Europe, with a number of debt-laden nations pinpointed at risk.
On Wednesday, credit rating agency Standard & Poor's cut its ratings on Spain by one notch to AA from AA-plus, saying a longer-than-expected period of low growth could undermine efforts to cut the budget deficit.
A day earlier, S&P had cut Greece's credit rating to junk bond status and slashed its ratings on Portugal.
George Papandreou, the Greek prime minister, said on Friday that his country's survival was the "red line" he would not cross during the crisis talks.
"Today what is most important is the survival of the nation, that is our red line," he told politicians at parliament.
"The measures which we must take, economic measures, are necessary for the protection of our country, for our survival, for our future so that we can stand firmly on our feet," he said.
A government source told the AFP news agency that the joint EU-IMF bailout agreement would be announced by Sunday.
Last week Greece asked the EU and IMF to activate a three-year rescue package worth $60bn this year alone as it faces a May 19 deadline to repay 9bn euros ($12bn) in maturing debts.
Eurozone finance ministers will meet in Brussels on Sunday where they will announce a figure for emergency loans for Greece until 2012, a spokesman for the chairman of the meeting said on Friday.
It is hoped the deal will help avoid a debt default that could also threaten countries such as Portugal and Spain.
Officials from the IMF, EU and European Central Bank are already holding talks in Athens, the Greek capital, to help negotiate the deal.
"The Greek people are realising that they will pay a heavy price for such a rescue"
Barnaby Phillips, Al Jazeera's correspondent in Athens, said: "Some sources are saying that Greece may get as much as 120bn euros spread over the next three years," he said.
"But the Greek people are realising that they will pay a heavy price for such a rescue.
"One newspaper this morning said: 'A nightmare that's unavoidable'."
He said the "bleak series" of spending cuts will include tax rises, big pay cuts in the public sectors and the potential for pay cuts and job losses in the private sector.
But many Greek citizens are up in arms over the proposed cutbacks, sparking dramatic protests on Thursday.
Our correspondent said there were fears that as "austerity measures really bite and as the recession continues, the anger on the streets could grow with severe political consequences".