(Reuters) - German Finance Minister Wolfgang Schaueble has joined Chancellor Angel Merkel in rebuking the leader of the junior coalition party over his tough talk on aid for debt-ridden Greece, keeping tensions within the government simmering.

According to the chancellor's guidance the finance minister is responsible for the euro, Schaueble told the Sunday newspaper Bild am Sonntag. I can't change the fact that many others are also commenting, he added.

Free Democratic Party leader (FDP) Philipp Roesler, the economy minister, sought to distance himself from Merkel's European strategy this week by saying an orderly bankruptcy of Greece should not be a taboo.

His remark jolted financial markets and prompted a public slap-down from Merkel, but may have also helped the FDP gain a little more support in an opinion poll on Friday.

The head of the FDP's parliamentary group, Rainer Bruederle, said in an interview with the Frankfurter Allgemeinen Sonntagszeitung that it was one of the foundations of a coalition government that decisions be taken within the cabinet.

In another sign of discord the leader of Germany's Christian Social Union (CSU), the conservative party governing the state of Bavaria, reiterated in an interview with Spiegel magazine that Greece might have to leave the euro zone if it failed to meet conditions set for bailouts.

If the Greek government and parliament cannot or will not keep to the path then we should not wait for the financial markets to force us into accepting reality. Then an exit of Greece from the euro zone must be conceivable, he said.

The head of the Social Democrats, the largest opposition party, told the Sunday edition of Berlin daily Tagesspiegel that Merkel could no longer govern with her existing coalition, given the unpredictable nature of the FDP's response.

Greek Prime Minister George Papandreou cancelled a planned visit to the United States on Saturday to deal with a deepening crisis at home, days before international inspectors arrive to go over fiscal shortfalls. (Reporting by Alexandra Hudson; Editing by Mark Heinrich)