Bill Gross, who runs the world's biggest bond fund at Pacific Investment Management Co., said Greece is heading for default.

The downgrade of European ratings by Standard & Poor's last week shows countries can fail to meet their debt obligations, Gross said in a Twitter posting. Greece will prove to be the latest example, Gross wrote.

Greek officials will meet with lenders on January 18 after discussions stalled last week over the size of investor losses in a proposed debt swap, raising the threat of default. European officials and creditors plan a 50 percent cut in the face value of Greek debt by voluntarily exchanging outstanding bonds for new securities, though the two sides haven't been able to agree on the coupon and maturity of the new debt.

German Chancellor Angela Merkel and French President Nicolas Sarkozy will also meet as the European Central Bank warns governments against "watering down" a revamp of budget laws.