European shares fell on Tuesday after Standard & Poor's warned it might downgrade 15 of the 17 euro zone countries, including Germany and France, if EU leaders cannot come up with a solution to the region's debt crisis at Friday's summit.

Banks, a focus in the euro zone debt crisis due to their exposure to sovereign debt, were amongst the main fallers, with the STOXX Europe 600 Banks index <.SX7P> down 1.1 percent and the STOXX Europe 600 Euro Zone Banks index <.SX7E> down 1.1 percent.

By 08183 GMT, the pan-European FTSEurofirst 300 <.FTEU3> index of top shares was 0.5 percent lower at 988.03 points after gaining 10.4 percent in the past week on hopes a plan was coming together to solve the euro zone debt crisis.

S&P is just reminding everyone the problems are still there in the euro zone and it is going to have a real impact on these countries, Joe Rundle, head of trading at ETX Capital, said.

It is a reality check, but I do not think all the gains from last week will be given up as the market could think it (the S&P move) could push the euro zone into action. (Reporting by Joanne Frearson)