Stock indices closed lower on concerns over the possible Greek default. The weekend's debt talks between Greece and its creditors were unsuccessful. An EU Commission official said that there are still big differences between the Greek reform plan and the demand of the creditors.

European Commission President Jean-Claude Juncker noted that a new debt deal could be reached until the end of the month.

The next round of talks is scheduled to at the finance ministers' meeting this Thursday in Luxembourg.

European Central Bank (ECB) President Mario Draghi said on Monday before the European Parliament's Economic and Monetary Affair's Committee that the ball lies in Athens' court to act. He noted that a "strong and comprehensive agreement" between Greece and its creditors was needed as soon as possible.

Standard & Poor's (S&P) said on Monday that it would not downgrade Greece's credit rating even if the country failed to meet the payment deadline in July and August.

Standard & Poor's downgraded its outlook on the U.K.'s credit rating to negative on Friday.

Indexes on the close:

Name Price Change Change %

FTSE 100 6,710.52 -74.40 -1.10 %

DAX 10,984.97 -211.52 -1.89 %

CAC 40 4,815.36 -85.83 -1.75 %