Standard & Poor's, the rating agency, warned the euro-area region's nations with a possible credit rating cut in case European leaders fail to quell jitters and tackle the debt crisis during the coming summit this week.

The agency also explained that European leaders must reach an agreement on how to solve the two-year debt crisis during the summit this week.

The Agency has placed the debt rating of 15 nations of the euro zone on a negative review, as S&P's said systemic stresses are growing up, while credit conditions tighten in the euro zone.

Germany, Austria, Belgium, Finland, Luxembourg and the Netherlands could face cuts of only one notch, while the other nine nations could face cuts of two notches, according to S&P's.

Cyprus and Greece were excluded from the watch negative, where Cyprus is already on credit watch negative, while Greece is rated CC -Junk-.

S&P said in a statement systemic stresses in the euro zone have risen in recent weeks to the extent that they now put downward pressure on the credit standing of the euro zone as a whole.

The agency typically downgrade the nations' credit rating in no more than three months after it put the nations under negative watch; however, the agency stressed that the review will be concluded as soon as possible following the European summit on Friday.